The Church of San Pietro was mentioned for the first time in the Liber Notitiae Sanctorum Mediolani at the end of the thirteenth century; it underwent several renovations: the current structure, except for some additions and subsequent modifications, dates back to the fifteenth century.

The small church is located in the medieval center of Buccinigo, near the place where the ancient castle of the village once stood; today it is surrounded by a courtyard and leaning against its buildings: for this reason it does not have a facade. It is accessed through a side door located above street level; this door is surmounted by a fake mullioned window with frescoes.

The single bell gable bell tower is placed on the roof of the religious building and the adjacent one.

The interior of the oratory consists of a single nave hall, divided from the presbytery by an ogival arch; the latter area leads to the sacristy, added following the pastoral visit of Cardinal Federico Borromeo in 1615. The frescoes preserved in San Pietro were made by different hands and in different periods.

The oldest is located near the entrance door, on the counter-façade: the fourteenth-century image depicts a holy bishop. Also on the counter-façade there is an oil on canvas, Jesus and the apostles, a seventeenth-century work by Giuseppe Vermiglio (1585-1635). On the right side of the hall is the chapel of Santa Caterina, once the patronage of the noble Carpani family. It has a sixteenth-century phytomorphic decoration with angels, cherubs, coats of arms and an Annunciation in monochrome tondi; inside there is a recently made work depicting Saint Catherine of Alexandria.

The vault of the presbytery area, adorned with a false coffered ceiling open to a sky from which the dove of the Holy Spirit descends, was lowered in an unspecified period: this can be seen from the mural paintings on the back wall, cut in the part superior.

The most important cycle, due to its extension, is located on the back wall. In the center there is a Crucifixion with the Virgin, Magdalene and John the Baptist, flanked on both sides by Saint Catherine of Alexandria and Saint Peter, above which an Annunciation remains; the announcing Angel on the opposite side is not preserved.

These frescoes bear the signature of Giovanni Andrea De Magistris: “io andreas de magistris cumarum pinxit”; they were probably made by concealing previous paintings, as can be seen from the fragments under the figure of St. Peter and from the inscription on his left: “mcccclxxxii die xxii iunij andreas filius magistri zentilini habitatoris cumarum pinxit”. In the lower band, an imitation marble decoration houses two tondi that enclose the busts of San Cassiano and San Pietro martire.

Near the access door to the sacristy, a box encloses a Madonna enthroned with Child and the saints Stephen and Anthony the Abbot.

Returning to the hall, on the arch of access to the presbytery, Saint Nicholas of Tolentino is crowned by Saints Cassiano and Donato and by the Virgin and Saint Catherine; at his feet the clients prostrate themselves.

On the wall opposite the chapel of Santa Caterina, two Madonnas enthroned with Child are represented; the figure on the left is connoted as Immaculate (she has the moon under her feet) and has a heart in her hand, probably a reference to a sixteenth-century heresy: Averroè claimed that Christ was conceived from three drops of blood coagulated in the heart of the Virgin. Near the entrance door, the white marble stoup welcomes the faithful; an inscription is engraved on it: “☩ d ns petrvs ordinarivs 14☩70”.