Alaungsithu or Sithu I (also Cansu I; 1089–1167) is king of the Pagan Dynasty of Burma (Myanmar) from c. 1112 to 1167.

Sithu's reign is a prosperous one in which Pagan is an integral part of inland and maritime trading networks.

Sithu engages in a massive building campaign throughout the kingdom, which includes colonies, forts and outposts at strategic locations to strengthen the frontiers, ordination halls and pagodas for the support of religion, as well as reservoirs, dams and other land improvements to assist the farmers.

He also introduces standardized weights and measures throughout the country to assist administration as well as trade.

He presides over the beginning of a transition away from the Mon culture toward the expression of a distinctive Burman style.

Sithu is remembered a peripatetic king who traveled extensively throughout his realm, built monuments and nurtured Theravada Buddhism with acts of piety.