Though built in the Pre-Romanesque period, only three windows from that original structure are preserved in the upper part of the walls (two in the south wall and one in the west wall). They recall those that illuminate the central nave of San Salvador de Valdediós. They are made of a monolithic block in which two horseshoe arches are carved, supported on a central column and two side semi-columns, above which there are three oculus windows cut out of the stone.
The church is rectangular in shape with two side chapels that form a sort of transept, and a square apse with two adjoining vestries, a room adjoining the north wall, and the chapter house, closed on the west side and open on the south side.
The nave is covered by an exposed wooden frame, the apse and north chapel, with stellar vaulting, while the south chapel is covered with ribbed groin vaulting. All these vaults conserve traces of 16th-century paintings, especially the main chapel.
It has two portals; the south is very simple, with a semi-circular arch, canopy and smooth imposts, while in the west portal, the semi-circular arch is flanked by two semi-columns supporting a triangular pediment and pinnacles.
