The move marked the latest sign of the growing rivalry between the two technology companies, close on the heels of Apple's decision to dump Google's mapping software from its devices.
"Our license to include the YouTube app in iOS has ended," Apple said in a statement on Monday. "Customers can use YouTube in the Safari browser and Google is working on a new YouTube app to be on the app store."
Google was not immediately available for comment.
YouTube has been among a handful of apps that come pre-loaded onto the screens of Apple's mobile devices since the original iPhone was introduced in 2007.
News of YouTube's disappearance from Apple's mobile software came as Apple released a new test version on Monday of the iOS 6 software, which for the first time did not include the YouTube app. The final version of iOS 6 is due for release sometime in the Fall.
Shares of Google were up $2.52 at $643.85 in late trading on Monday. Apple shares were up $7.74 at $623.47.