Konstantios Doukas (Greek: Κωνστάντιος Δούκας, 1060 – 18 October 1081), Latinized as Constantius Ducas, was a junior Byzantine emperor from 1060 to 1078.

[2] Konstantios retained his title of junior emperor during the reigns of Constantine (1060–1067), Romanos IV Diogenes (1068–1071), and Michael VII (1071–1078).

[5] Michael VII chose Konstantios to succeed him, as Andronikos had died a few years before this or he wasn't interested to throne.

[11] Later that year an Anatolian army rebelled in favour of Konstantios, but it was quickly defeated by Nikephoros' forces.

During this engagement, the Varangian Guard, with whom Konstantios was fighting, was separated from the core body of the Byzantine army and massacred.

[13] Due to the limited sources for Konstantios' life, he's often confused with his younger nephew, the porphyrogennetos Constantine Doukas.

[11] Konstantios Doukas is thought to be engraved on the Holy Crown of Hungary, which was given to King Géza I of Hungary (r. 1074–1077) by Konstantios' brother Michael VII, depicted alongside King Geza I and Michael VII;[14] although some argue that it actually depicts Constantine Doukas.