Cathedral Museum is a museum that has a collection of objects of Catholics that explain the history and development of Catholicism in the archipelago. The museum was inaugurated on 28 April 1991 by Mgr Julius Darmaatmaja. The construction of the Cathedral museum was initiated by the cathedral priest at that time, Peter Rudolf Kurris. It originated from Kurris's love of history and historic objects. This Cathedral Museum is in the cathedral balcony room.
Interestingly, in this museum, visitors will find the work of Romo Reksaatmadja in the era of the 1930s in the form of carving statue of Our Lady berkonde. This statue has the meaning of the Virgin Mary is a reflection of Indonesian culture as one of the originators of Catholic art. There is also a painting of a tree trunk by Kusni Kadut, a high-profile criminal who was executed in 1980.