The decoration of the naves is simple, the main one finishes off in a reduced cannon vault in Colonial red painted wood with gilded moldings and is finished off with an entablature decorated with triglyphs and separated by large pillars made in wood and covered in cement to form a column. In the entrance there is an atrium also supported by two columns in a Corinthian style and bordered by a balustrade, where the main organ is located. The lateral naves have a lintel top, also painted in Colonial red.

The lighting of the church is through the candelabra located in the central part of each semicircular arch separating the naves.

The high altar is located in the central nave deep apse and visitors cannot visit that area. It is in a Baroque style made of carved wood, lighted by a gabled skylight that ends in a lantern found in the top part. The figure of the Patron Saint of the Church, Our Lady of el Monte de la Cabeza crowns the altar. There is no exact date for the arrival of the figure to Chile. There are two versions, one that it was brought to Chile in 1633 by the Franciscan priests and the other that it came in 1605. The apse is decorated with a variety of fabrics placed on the lateral walls, with scenes from the bible and saints. Its preservation condition is precarious.

The lateral naves have a series of beautifully styled altars, made of polychrome wood in a Baroque – Bavarian style, which are exempt from construction and are crowed by the semicircular arches developed in the temple architecture. Looking towards the high altar from the left lateral nave, there are: the Nazarene of Great Power, representing Jesus carrying the cross on his shoulder; Santa Philomena, an altar designed by the architect Fermín Vivaceta and that has in the back, to the left, the tomb with the human remains of Fray Andresito venerated in this temple; Santa Clara, a sculpture located in an architectonic altar; the side chapel is located on the side of the high altar containing sculptural figures of guardian angels protecting the Holy Sacrament.

Historical polychrome wood sculptural figures of Saint Buenaventura and Saint Luis de Tolosa accompany the side chapel and a there is a small art work dedicated to the Sacred Heart of Jesus. On the right side there is an architectonic altar dedicated to San Francisco; Saint Antonio; Saint Judas Tadeo; Santa Teresa de los Andes; Santa Margarita de Cortona, Patron Saint protector of dogs and cats; and the altar dedicated to the Crucifixion, all made in polychrome wood sculptures.