Constantine I or Kostandin I (1035–1040 / 1050–1055 – c. 1100/ February 24, 1102 – February 23, 1103) is the second lord of Armenian Cilicia or “Lord of the Mountains” (1095 – c. 1100 / 1102 / 1103).

During his rule, he controls the greater part of the regions around the Taurus Mountains, and invests much of his efforts in cultivating the lands and rebuilding the towns within his domain.

He provides ample provisions to the Crusaders, for example during the difficult period of the siege of Antioch in the winter of 1097.

He is a passionate adherent of the separated Armenian Church.