The church of Sant'Agostino stands near the Augustinian convent. It was built between 1280 and 1298 and was made entirely of bricks to make it very simple and austere. The architectural style includes features of both Romanesque and Gothic architecture. The facade has a single opening and a rose window decorated in terracotta at the top. A small door on the side provides access to the interior.
The church has a single large nave with a wooden trussed ceiling and ends in the presbytery with a central chapel and two smaller lateral ones. The beautiful Chapel of San Bartolo makes it one of the most beautiful small churches in the whole of Tuscany. The Renaissance chapel is dedicated to the saint from San Gimignano and is located in the counter-facade of the church. The precious white marble altar, made by Benedetto da Maiano, is decorated with the story of the miracles of San Bartolo and contains the remains of the saint. Above the composition, there is a Madonna with Child and two angels. On the wall to the left of the chapel, there are frescoes of saints Gimignano, Lucy and Nicholas. The vault was frescoed by Sebastiano Mainardi, Ghirlandaio's brother-in-law. The floor is also very beautiful and completely original, made of majolica tiles by Andrea della Robbia.
On the walls of the nave, there are several works of great value, including a fresco by Benozzo Gozzoli depicting Saint Sebastian with worshippers, dating back to 1464.