∵四边形ABCD是正方形,
∴∠CAB=∠BCA=45°;
△ACE中,AC=AE,则:
∠ACE=∠AEC= (180°-∠CAE)=67.5°;
∴∠BCE=∠ACE-∠ACB=22.5°.
故答案为22.5.