The Sacristy dates back to 1622 and is a work that combines Mannerism and Baroque style characteristics. Its layout is authored by Pedro Tinoco, an architect from Lisbon.

The dome is magnificent and the 17th century tiles mimic the Persian tapestryThis Sacristy can be considered to be a small museum due to the presence of very valuable pieces of art, such as the Pentecostes by Grão Vasco, the Ecce Homo and the Calvary by Cristovão de Figueiredo, as well as the large canvas called Descimento da Cruz, by André Gonçalves.

Other important objects are on display too, such as an 18th century framed mirror and huge wooden images from the 19th century: Our Lady and St. John the Evangelist next to the cross, and St. Gudula and St. Gertrude.

There is also a chest of drawers with ivory inlays that go along the length of the entire Sacristy. This chest of drawers was created by Samuel Tibau in the 17th century.

Next to the door that gives access to the Chapter Room, there is the Amictuário, which is a type of closet that contains, in each of the lockers, some ivory plates and the identification of the last friars that used them.