Delete messages and conversations in Messages on Mac
Messages saves your conversations automatically, so even if you turn off your Mac or start using another device, you can pick up where you left off. However, you can delete messages and entire conversations.
Set how long to keep messages
In the Messages app on your Mac, choose Messages > Preferences, then click General.
Click the “Keep messages” pop-up menu, then choose an option.
Important: If you choose an option other than Forever, your conversations (including all attachments) are automatically removed after the specified time period elapses.
Delete a message
In the Messages app on your Mac, select a conversation.
Do any of the following to delete one or more messages:
Delete all messages within a conversation: Choose Edit > Clear Transcript.
The conversation remains in your sidebar, but all content is removed from the transcript.
Delete a conversation
Note: You can’t recover a deleted conversation.
In the Messages app on your Mac, search for a conversation.
Do any of the following to delete a conversation:
Delete an empty conversation: Move the pointer over an empty conversation, then click the Close button .
Delete a conversation: Select a conversation, then choose File > Delete Conversation. Or if you have a trackpad or Magic Mouse, you can also swipe left with two fingers on the conversation in the sidebar, then click the Delete button .
If you use Messages in iCloud, deleting a conversation on your Mac deletes it from all your devices where Messages in iCloud is turned on. See Access your messages on all your Apple devices.