Speaking on BBC Radio 2, Peter said: "I feel itâ€™s time to move on."
The new series airs in spring and Capaldi said his final episode will be shown at Christmas.
The 58-year-old Glasgow-born star became the 12th actor to play the Doctor in 2013.
He's shared his adventures with Clara Oswald (Jenna Coleman) and Bill Potts (Pearl Mackie)
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He was a good doctor to be honest, however if you read the chronicles of Doctor Who and it states that there should have been only 12 regenerations. And so there can't be a new doctor. I am sad to see him go because he really made a impact on the Doctor Who series and I just don't think there should be anymore since this is the Doctor's last regeneration.
William, Sheffield, England
I think Martin Freeman should be the next doctor. He would be really good at it and he would be really funny.
Alice, Weymouth, England
I think the next actor to play the doctor should definitely be a man. My dad and I think it should be British actor Simon Pegg.
Joshua, United Kingdom
I would like to be the next doctor!
William, Okehampton, England
I agree that Peter made a good choice so he can move on to other things. I also think that next doctor should be a woman.
Sophie, Surrey, England
Sad news for fans of Peter Capaldi - he's leaving Doctor Who at the end of the year, it's been announced.