Depp and Richards shared the screen in the 2007 film Pirates of the Caribbean: At World's End.
In an interview with Radio Times, Depp said that he treasures the time he spends with the Rolling Stones guitarist.
"He's a fascinating man, you know. Read his autobiography Life. It's a great book, and he tells it like it is," Depp said about Richards.
The Oscar nominee continued: "I've known him for a long time. To get periods on set where it's just him and me hanging out, sitting around and yakking about music, movies, whatever, was a real pleasure."
Depp, who will appear in the film adaptation of 21 Jump Street, also joked that Richards would drink something that "looks like nuclear waste" to unwind.
"I'm a wine man and I do like a good glass of red. So I would have my glass of wine and Keith would have his usual. I've no idea what that is, because it looks like nuclear waste and it's a combination only he would know," he added.
Richards and Depp will appear together on the next Pirates movie On Stranger Tides, opening May 20, 2011.
View the trailer for Pirates of the Caribbean: On Stranger Tides below: