The Sanctuary of Bona Dea in the Regio V, X, 2 is one of the two temples dedicated to the goddess in Ostia. It’s one of the oldest sanctuaries found in the city, that yielded three dedicatory inscriptions offered by three female worshippers and donors, named Octavia, Valeria Hetera and Terentia, which cover a time span from the I century B.C. until the I century A.D. The recently edited study on the adjacent Terme del Nuotatore (Baths of the Swimmer) has offered the opportunity for a new analysis of the Sanctuary’s building phases, nine in total. An in-depth survey has been carried out in two entrance-hallways, one leading to the Sanctuary and the second conducting to the Baths. The picture that emerges from the survey enables us to undestand in detail the architectural evolution of the Sanctuary, consisting in various increases of floor levels and consequent renovation of the wall frescoes. Besides the survey has shown that the Sanctuary was completely abandoned and filled up, probabily in the IV century A.D., just as it happened to the other Bona Dea sanctuary in Ostia.