The patron saint of Diano San Pietro is Saint Peter, celebrated on 29 June, in the parish church dedicated to him in the main town. The earlier building certainly had medieval origins, but the present reconstruction dates from the late 18th century: inside, besides the marble altars inherited from the earlier church, are preserved a painting attributed to Giovanni Battista Paggi, another by his pupil Giovanni Domenico Cappellino, and a 17th-century marble pulpit.
The town also preserves the 19th-century parish church of the Nativity of the Virgin Mary, in the hamlet of Borganzo, which houses a 1518 polyptych by Antonio Brea, and that of Santa Maria Assunta e Santa Lucia, in the hamlet of Roncagli, from the 17th century. Along the left bank of the San Pietro stream, which gives the town its name, traces of walls probably belonging to a Roman imperial-era villa have been found.
