Constantine Laskaris (Greek Κωνσταντίνος Λάσκαρης) was Byzantine Emperor for a few months from 1204 to early 1205.

Constantine Laskaris was born of a noble but not particularly renowned Byzantine family. Virtually nothing is known of him prior to the events of the Fourth Crusade. He found favour after his brother Theodore married into the imperial family, becoming the son-in-law of Emperor Alexius III.

During the first siege of Constantinople in 1203 he was given command of the best body of troops available and led the Greek defenders on sorties against the entrenched Crusaders. None were successful in their goal of lifting the siege, and finally Constantine was ordered to attack the Burgundians who were on guard at the time.

The Greeks issued forth from the city, but were soon driven back to the gates, notwithstanding the stones that the defenders on the walls threw down onto the advancing Crusaders. Constantine himself was captured whilst mounted on his horse by William of Neuilly and probably kept for ransom, which was the usual practice of the times. At some point he was released, as he was soon swept up in the events of the second siege of Constantinople in 1204.