This function was totally changed in 2015 following the described architectural research. In the post-war times of the 20th century the basement with a cellarium fragment served as a handy storage of the convent. Another modernization of the cellar took place probably in about 1909 when a large boiler room was built in the east and concrete floor, a small pool with drainage tubes to collect ground water were built as well as a stove was put there to dry the interior. Then, on the ground floor of the northern cloister a monastic chapel was arranged and under it in the cellar a boiler room was probably placed. A change in the function of the cellar took place in about 1894 after the secularization of the Cistercian convent and was connected with the beginning of the functioning of the Congregation of the Sisters of Charles Borromeo. At that time a small cellar was created in the northern part of the cellarium. The first reconstruction of the cellarium took place in around 1706 and it was connected with the construction of the great Baroque building of the Cistercian enclosure. It was probably erected in the years 1203–1214. It performed the function of an everyday storage of the Cistercian convent. The cellarium was a two-aisle room covered with a cross vault supported by brick arches and a stone pillar. Its western wall was at the same time a part of the facade of the western wing and its preserved fragment of the room is the only existing relic of the interior of the oldest convent in Trzebnica. The researched fragment is a remnant of the first enclosure building. The final part of the article constitutes an attempt to reconstruct and date transformations of the cellarium of the Trzebnica enclosure. After presenting a general history of the object and the state of the research, the scope of architectural and archaeological works was described separately. The article presents the results of the architectural and archaeological research which was conducted in 2015 in the basement with a fragment of the enclosure cellarium of the former Cistercian Abbey in Trzebnica.