Then Judas, which had betrayed him, when he saw that he was condemned, repented himself, and brought again the thirty pieces of silver to the chief priests and elders, 4Saying, I have sinned in that I have betrayed the innocent blood. And they said, What is that to us? see thou to that.
Matthew 27:3-4
He repented when he realize he was condemn of God and His law. Take note that his repentance did not lead him to believe in and confess Jesus as the Son of God or the Messiah. He just wanted to get out from under his condemnation.