diff --git a/.chloggen/14435.yaml b/.chloggen/14435.yaml
new file mode 100644
index 00000000000..9cf3ef229c9
--- /dev/null
+++ b/.chloggen/14435.yaml
@@ -0,0 +1,25 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. receiver/otlp)
+component: all
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: "Default `sending_queue::batch::sizer` to `items` when `sending_queue::sizer` is unset to avoid validation errors."
+
+# One or more tracking issues or pull requests related to the change
+issues: [14435]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []
diff --git a/exporter/exporterhelper/internal/queuebatch/config.go b/exporter/exporterhelper/internal/queuebatch/config.go
index 78569b85d82..47eb170de04 100644
--- a/exporter/exporterhelper/internal/queuebatch/config.go
+++ b/exporter/exporterhelper/internal/queuebatch/config.go
@@ -51,12 +51,15 @@ func (cfg *Config) Unmarshal(conf *confmap.Conf) error {
 	}
 
 	// If all of the following hold:
-	// 1. the sizer is set,
-	// 2. the batch sizer is not set and
-	// 3. the batch section is nonempty,
-	// then use the same value as the queue sizer.
-	if conf.IsSet("sizer") && !conf.IsSet("batch::sizer") && conf.IsSet("batch") && conf.Get("batch") != nil {
-		cfg.Batch.Get().Sizer = cfg.Sizer
+	// 1. the batch sizer is not set and
+	// 2. the batch section is nonempty,
+	// then use the same value as the queue sizer if set, otherwise default to items.
+	if !conf.IsSet("batch::sizer") && conf.IsSet("batch") && conf.Get("batch") != nil {
+		if conf.IsSet("sizer") {
+			cfg.Batch.Get().Sizer = cfg.Sizer
+		} else {
+			cfg.Batch.Get().Sizer = request.SizerTypeItems
+		}
 	}
 	return nil
 }
diff --git a/exporter/exporterhelper/internal/queuebatch/config_test.go b/exporter/exporterhelper/internal/queuebatch/config_test.go
index b43bb5aa073..246d7f73016 100644
--- a/exporter/exporterhelper/internal/queuebatch/config_test.go
+++ b/exporter/exporterhelper/internal/queuebatch/config_test.go
@@ -180,3 +180,14 @@ func TestUnmarshal(t *testing.T) {
 		})
 	}
 }
+
+func TestUnmarshalBatchSizerDefaultsToItemsWithoutParentSizer(t *testing.T) {
+	cm, err := confmaptest.LoadConf(filepath.Join("testdata", "batch_set_nonempty_no_parent_sizer.yaml"))
+	require.NoError(t, err)
+
+	var cfg Config
+	require.NoError(t, cfg.Unmarshal(cm))
+	require.NotNil(t, cfg.Batch.Get())
+	assert.Equal(t, request.SizerTypeItems, cfg.Batch.Get().Sizer)
+	require.NoError(t, xconfmap.Validate(cfg))
+}
diff --git a/exporter/exporterhelper/internal/queuebatch/testdata/batch_set_nonempty_no_parent_sizer.yaml b/exporter/exporterhelper/internal/queuebatch/testdata/batch_set_nonempty_no_parent_sizer.yaml
new file mode 100644
index 00000000000..381cc94b824
--- /dev/null
+++ b/exporter/exporterhelper/internal/queuebatch/testdata/batch_set_nonempty_no_parent_sizer.yaml
@@ -0,0 +1,5 @@
+num_consumers: 10
+queue_size: 1000
+batch:
+  flush_timeout: 1s
+  min_size: 100