Constance of Castile (Spanish Constanza) (1323 - November 13 1345) was the daughter of Juan Manuel "El Scritor" de Castile and Constanza of Aragon. She was the first wife of Alfonso XI of Castile (March 28 in Valladolid), which was annulled in 1327. She was the second wife of Pedro I of Portugal, marrying on August 24 1339 in Lisbon. They had three children:

• Luiz (February 27 1340 - March 6 1340)
• Maria (April 6 1343 - app. 1367)
• Fernando of Portugal (October 31 1345 - October 29 1383)