Constantine Dalassenos (Greek: Κωνσταντίνος Δαλασσηνός, romanized: Kōnstantinos Dalassēnos) was a prominent Byzantine aristocrat of the first half of the 11th century.

When Michael's successor was deposed in 1042, Zoe invited Dalassenos to an audience with a view to marrying him and making him emperor; displeased by his haughty manner she chose a more pliant man, Constantine IX Monomachos.

[1] He was the eldest son of the magistros Damian Dalassenos, who held the important post of doux of Antioch from 995 or 996 until his death in battle against the Fatimids at Apamea in 998.

[2][6] He reappears in spring 1024, when he held his father's old post as doux of Antioch, with the rank of patrikios, the Empire's senior honorific title, which was limited to a small number of holders.

Several prominent Anatolian families, notably the powerful Doukai, supported him; the later emperor Constantine X Doukas (r. 1059–1067) was married to Dalassenos's daughter.

Dalassenos at first refused, but after receiving assurances for his safety, guaranteed by an oath on some of the Empire's holiest relics, he left for the imperial capital.

[12][14] Initially he was treated well, receiving a promotion and gifts, but in summer 1034 a revolt broke out in Antioch against the local governor, Michael IV's brother Niketas.

[18] A later tradition has it that during Dalassenos's detention in the capital, Zoe, who had yet to conceive a child, carried out a secret relationship with him in hopes of getting pregnant.

[13][15] After Michael V was deposed in a popular uprising in April 1042, Constantine VIII's daughters Zoe and Theodora were left as de facto rulers of the Byzantine Empire.