After becoming an Ottoman land by Orhan Ghazi’s conquest between 1324 and 1326, Bolu has been reconstructed rapidly during the reign of Yildirim Bayezid. In addition to the public works, it has also started to revive economically, socially, and culturally. In this period, several architectural structures were built according to the needs of the city. Ak Masjid, which was built during the reign of Yildirim Bayezid is one of them. For the expenses of the masjid, foundation revenues were given at various times. After a while, the name of the mosque was given to the neighborhood where it was built. The masjid has suffered two major disasters, namely fire and earthquake. It was rebuilt after the fire but unfortunately was not possible to rebuild after the earthquake. Thus, the building has not survived to the present day. There is no detailed study that has been done on the structure previously. In this study, the changes and transformations of the building will be presented chronologically with the old photographs of the building, especially the Ottoman and Turkish Republic period documents in the Presidential Archives. The importance of the work in Turkish-Islamic architecture will be emphasized.[You may find an extended abstract of this article after the bibliography.]