The Palace of Mafra (Portuguese: Palácio de Mafra), also known as the Palace-Convent of Mafra and the Royal Building of Mafra (Real Edifício de Mafra), is a monumental Baroque and Neoclassical palace-monastery located in Mafra, Portugal, some 28 kilometres from Lisbon. Construction began in 1717 under King John V of Portugal and was completed in 1755.

The palace was classified as a National Monument in 1910 and was also a finalist in the Seven Wonders of Portugal. On 7 July 2019, the Royal Building of Mafra – Palace, Basilica, Convent, Cerco Garden and Hunting Park (Tapada) was inscribed as a UNESCO World Heritage Site.

The palace, which also served as a Franciscan friary, was built during the reign of King John V (1717–1750), as consequence of a vow the king made in 1711, to build a convent if his wife, Maria Anna of Austria, gave him offspring. The birth of his first daughter the Infanta Barbara of Portugal, prompted construction of the palace to begin. The palace was conveniently located near royal hunting preserves, and was usually a secondary residence for the royal family.

The construction was funded in large part from the proceeds of Colonial Brazil, where gold and then diamonds were mined in vast quantities.

This vast complex, largely built of Lioz stone, is among the most sumptuous Baroque buildings in Portugal and at 40,000 m², one of the largest royal palaces. Designed by the German architect João Frederico Ludovice, the palace was built symmetrically from a central axis, occupied by the basilica, and continues lengthwise through the main façade until two major towers. The structures of the convent are located behind the main façade. The building also includes a major library, with about 30,000 rare books. The basilica is decorated with several Italian statues and includes six historical pipe organs and two carillons, composed of 98 bells.

The exact site was chosen in 1713 and purchased in 1716. Construction began by the laying of the first stone on November 17, 1717, with a grand ceremony in the presence of the king, his entire court and the Cardinal Patriarch of Lisbon.

Initially it was a relatively small project for a friary of 13 Capuchin friars, who were to observe strict poverty. However, when the flow of gold and diamonds from the Portuguese colony of Brazil started to arrive in Lisbon in abundance, the King changed his plans and announced the construction of a sumptuous palace along with a much enlarged friary. This immense wealth allowed the King to be a generous patron of the arts.

He appointed an architect João Frederico Ludovice as director of the royal works at Mafra. Ludwig had studied architecture in Rome and knew contemporary Italian art. The extent of Ludwig's responsibility is unclear, as several other architects were involved in this project: the Milanese builder Carlos Baptista Garbo, Custódio Vieira, Manuel da Maia and even his own son António. However the application of the same architectural style over the whole building suggests the work of Ludwig as the head-architect in charge of the Royal Office of Works (Real Obra).