Your WhatsApp chats are automatically backed up and saved daily on your phone's memory. Depending on your settings, you can also periodically backup your WhatsApp chats to your Google Drive. If you uninstall WhatsApp from your phone but don't want to lose any of your messages, be sure to manually back up your chats before uninstalling:
To export a copy of the history of an individual chat or group, use the Email chat feature:
An email will be composed with your chat history attached as a .txt document.
Note:
Learn how to export your chat history on: iPhone | Windows Phone | Nokia S40 | BlackBerry | Nokia S60 | BlackBerry 10
Cheers,
WhatsApp Support Team