Constantine X Ducas was the emperor of the Byzantine Empire from 1059 to 1067. He came to power on the advice of Michael Psellus when Isaac I retired.

Constantine was married to Eudocia Macrembolitissa, the niece of Michael Cerularius. Eudocia dominated her husband's reign, as did Michael Psellus. He was unpopular with supporters of Isaac, who attempted to assassinate him in 1060; he was also unpopular with the general population, after he raised taxes to try to pay the army. Constantine lost most of Byzantine Italy to the Normans, except for the territory around Bari, and also suffered invasions from Alp Arslan in Asia Minor in 1064 and the Uzes in the Balkans in 1065. Already old and unhealthy when he came to power, he died in 1067 and was succeeded by his young son Michael VII.

Preceded by:
Isaac I
Byzantine emperors Followed by:
Michael VII