diff --git a/conf/defaults.ini b/conf/defaults.ini
index 28cd0420eb2..363ca39d0c4 100644
--- a/conf/defaults.ini
+++ b/conf/defaults.ini
@@ -1653,6 +1653,11 @@ loki_basic_auth_password =
 # Accepts duration formats like: 30s, 1m, 1h.
 rule_query_offset = 1m
 
+# Default data source UID to use for query execution when importing Prometheus rules.
+# This default is used when the X-Grafana-Alerting-Datasource-UID header is not provided.
+# If not set, the header becomes required.
+default_datasource_uid =
+
 [recording_rules]
 # Enable recording rules.
 enabled = true
diff --git a/conf/sample.ini b/conf/sample.ini
index 0bb5b82fdc9..530b14c87ac 100644
--- a/conf/sample.ini
+++ b/conf/sample.ini
@@ -1615,6 +1615,11 @@ max_annotations_to_keep =
 # Accepts duration formats like: 30s, 1m, 1h.
 rule_query_offset = 1m
 
+# Default data source UID to use for query execution when importing Prometheus rules.
+# This default is used when the X-Grafana-Alerting-Datasource-UID header is not provided.
+# If not set, the header becomes required.
+default_datasource_uid =
+
 #################################### Recording Rules #####################
 [recording_rules]
 # Enable recording rules.
diff --git a/docs/sources/alerting/alerting-rules/alerting-migration.md b/docs/sources/alerting/alerting-rules/alerting-migration.md
index 3afa3aec453..ab2a5e995cd 100644
--- a/docs/sources/alerting/alerting-rules/alerting-migration.md
+++ b/docs/sources/alerting/alerting-rules/alerting-migration.md
@@ -242,6 +242,8 @@ Set to `true` to import recording rules in paused state.
 
 The UID of the data source to use for alert rule queries.
 
+If not specified in the header, Grafana uses the configured default from `unified_alerting.prometheus_conversion.default_datasource_uid`. If neither the header nor the configuration option is provided, the request fails.
+
 #### `X-Grafana-Alerting-Target-Datasource-UID`
 
 The UID of the target data source for recording rules. If not specified, the value from `X-Grafana-Alerting-Datasource-UID` is used.
diff --git a/docs/sources/setup-grafana/configure-grafana/_index.md b/docs/sources/setup-grafana/configure-grafana/_index.md
index 05d9cb66228..67c361b2bdc 100644
--- a/docs/sources/setup-grafana/configure-grafana/_index.md
+++ b/docs/sources/setup-grafana/configure-grafana/_index.md
@@ -2052,6 +2052,10 @@ This section applies only to rules imported as Grafana-managed rules. For more i
 
 Set the query offset to imported Grafana-managed rules when `query_offset` is not defined in the original rule group configuration. The default value is `1m`.
 
+#### `default_datasource_uid`
+
+Set the default data source UID to use for query execution when importing Prometheus rules. Grafana uses this default when the `X-Grafana-Alerting-Datasource-UID` header isn't provided during import. If this option isn't set, the header becomes required. The default value is empty.
+
 <hr>
 
 ### `[annotations]`
diff --git a/pkg/services/ngalert/api/api_convert_prometheus.go b/pkg/services/ngalert/api/api_convert_prometheus.go
index 79198ababf1..b6849f55dfc 100644
--- a/pkg/services/ngalert/api/api_convert_prometheus.go
+++ b/pkg/services/ngalert/api/api_convert_prometheus.go
@@ -375,6 +375,9 @@ func (srv *ConvertPrometheusSrv) RouteConvertPrometheusPostRuleGroups(c *context
 	}
 
 	datasourceUID := strings.TrimSpace(c.Req.Header.Get(datasourceUIDHeader))
+	if datasourceUID == "" {
+		datasourceUID = srv.cfg.PrometheusConversion.DefaultDatasourceUID
+	}
 	if datasourceUID == "" {
 		return response.Err(errDatasourceUIDHeaderMissing)
 	}
diff --git a/pkg/services/ngalert/api/api_convert_prometheus_test.go b/pkg/services/ngalert/api/api_convert_prometheus_test.go
index b4377431249..74e851ed195 100644
--- a/pkg/services/ngalert/api/api_convert_prometheus_test.go
+++ b/pkg/services/ngalert/api/api_convert_prometheus_test.go
@@ -75,6 +75,46 @@ func TestRouteConvertPrometheusPostRuleGroup(t *testing.T) {
 		require.Contains(t, string(response.Body()), "Missing datasource UID header")
 	})
 
+	t.Run("without datasource UID header but with config default should succeed", func(t *testing.T) {
+		srv, _, ruleStore := createConvertPrometheusSrv(t)
+		// Set the config default
+		srv.cfg.PrometheusConversion.DefaultDatasourceUID = existingDSUID
+
+		rc := createRequestCtx()
+		rc.Req.Header.Set(datasourceUIDHeader, "")
+
+		response := srv.RouteConvertPrometheusPostRuleGroup(rc, "test", simpleGroup)
+
+		require.Equal(t, http.StatusAccepted, response.Status())
+
+		// Verify that the config default datasource was used
+		assertRulesUseDatasource(t, ruleStore, existingDSUID, 2)
+	})
+
+	t.Run("header should take precedence over config default", func(t *testing.T) {
+		srv, dsCache, ruleStore := createConvertPrometheusSrv(t)
+		// Add another datasource
+		anotherDS := &datasources.DataSource{
+			UID:  "another-ds",
+			Type: datasources.DS_PROMETHEUS,
+		}
+		dsCache.DataSources = append(dsCache.DataSources, anotherDS)
+
+		// Set the config default to one DS
+		srv.cfg.PrometheusConversion.DefaultDatasourceUID = "another-ds"
+
+		// But use the header to specify a different one
+		rc := createRequestCtx()
+		rc.Req.Header.Set(datasourceUIDHeader, existingDSUID)
+
+		response := srv.RouteConvertPrometheusPostRuleGroup(rc, "test", simpleGroup)
+
+		require.Equal(t, http.StatusAccepted, response.Status())
+
+		// Verify that the header datasource was used, not the config default
+		assertRulesUseDatasource(t, ruleStore, existingDSUID, 2)
+	})
+
 	t.Run("with invalid datasource should return error", func(t *testing.T) {
 		srv, _, _ := createConvertPrometheusSrv(t)
 		rc := createRequestCtx()
@@ -1761,6 +1801,26 @@ func createRequestCtx() *contextmodel.ReqContext {
 	}
 }
 
+// assertRulesUseDatasource retrieves all alert rules from the store and verifies they use the expected datasource
+func assertRulesUseDatasource(t *testing.T, ruleStore *fakes.RuleStore, expectedDatasourceUID string, expectedRuleCount int) {
+	t.Helper()
+
+	rules, err := ruleStore.ListAlertRules(context.Background(), &models.ListAlertRulesQuery{
+		OrgID: 1,
+	})
+	require.NoError(t, err)
+	require.Len(t, rules, expectedRuleCount)
+
+	for _, rule := range rules {
+		if rule.Record == nil {
+			require.NotEmpty(t, rule.Data)
+			require.Equal(t, expectedDatasourceUID, rule.Data[0].DatasourceUID, rule.Title, expectedDatasourceUID)
+		} else {
+			require.Equal(t, expectedDatasourceUID, rule.Record.TargetDatasourceUID)
+		}
+	}
+}
+
 // Test parseBooleanHeader function which handles boolean header values
 func TestParseBooleanHeader(t *testing.T) {
 	headerName := "X-Test-Header"
diff --git a/pkg/setting/setting_unified_alerting.go b/pkg/setting/setting_unified_alerting.go
index 0733e8241e6..743f386ff52 100644
--- a/pkg/setting/setting_unified_alerting.go
+++ b/pkg/setting/setting_unified_alerting.go
@@ -190,6 +190,8 @@ type UnifiedAlertingReservedLabelSettings struct {
 type UnifiedAlertingPrometheusConversionSettings struct {
 	// RuleQueryOffset defines a time offset to apply to rule queries during conversion from Prometheus to Grafana format
 	RuleQueryOffset time.Duration
+	// DefaultDatasourceUID is the default datasource UID to use when converting Prometheus rules if not specified via header
+	DefaultDatasourceUID string
 }
 
 type UnifiedAlertingLokiSettings struct {
@@ -536,7 +538,8 @@ func (cfg *Cfg) ReadUnifiedAlertingSettings(iniFile *ini.File) error {
 
 	prometheusConversion := iniFile.Section("unified_alerting.prometheus_conversion")
 	uaCfg.PrometheusConversion = UnifiedAlertingPrometheusConversionSettings{
-		RuleQueryOffset: prometheusConversion.Key("rule_query_offset").MustDuration(time.Minute),
+		RuleQueryOffset:      prometheusConversion.Key("rule_query_offset").MustDuration(time.Minute),
+		DefaultDatasourceUID: prometheusConversion.Key("default_datasource_uid").MustString(""),
 	}
 
 	rr := iniFile.Section("recording_rules")