He made the claim in a tweet a day after their final debate.
Why didn't Hillary Clinton announce that she was inappropriately given the debate questions - she secretly used them! Crooked Hillary.
Although Trump did not specify he was referring to Wednesday evening's debate, the timing of the tweet suggests that was his intention.
During that third and final presidential debate, moderator Chris Wallace made clear that he had not shared his questions ahead of time.
"For the record, I decided the topics and the questions in each topic. None of those questions has been shared with a commission or the two candidates," the Fox News anchor said, according to a transcript of the event.
Clinton's campaign did not immediately respond to a request for comment.
Some outlets have reported that a Democratic National Committee official may have provided a single question to the Clinton campaign ahead of a town hall event during the primary campaign. Those allegations were denied by that official.