Mazaleón (also known as Massalió) is a municipality in the province of Teruel, in the Aragon region of Spain. It is located in the Matarraña/Matarranya comarca, a district in the eastern part of the province near the border with Catalonia.
According to the 2004 census conducted by the Instituto Nacional de Estadística (INE), the municipality had a population of 587 inhabitants. The dual name reflects the area's linguistic heritage, with "Mazaleón" being the Spanish form and "Massalió" the Catalan form used locally.