Polychrome on the vaults or walls of grave crypts are a rare category of finds and they are often accompanied by problems for specialist analyses or restoration. A composition of five images of religious and symbolic character was registered on a completely plastered barrel vault with lunettes in a crypt situated under the chapel of The Passion in postcistercian church of The Holy Trinity in Byszewo. Archaeological exploration of the crypt resulted in the excavation of 92 coffins of lay representatives – both adults and children. Burial and grave goods analyses confirmed that the crypt could have been erected in the middle of 18th century and used until the beginning of 19th century. Physicochemical tests and conservation analysis of the painting suggest that walls and the vault completing works could be continued in the time of intense use of the room as a burial place, and the present polychrome is probably the fourth layer of painting. The elements preserved until the present day might have been created between the 18th and 19th century.