St. Peter's Church is divided into three naves by three pairs of pilars that hold the brick vaults.

In the beginning of the 16th century the wooden ceiling inside the church was replaced with large brick vaults.

Not many objects were either confiscated to the Swedish Crown and no sculptures picturing saints were destroyed.

[2] Siuntio St. Peter's Church was badly damaged during the Great Northern War.

After the fire St. Peter's church was heavily modified following the eras architectural ideals in the Grand Duchy of Finland; the windows were enlarged and the pilars holding the medieval vaults were rounded.

In July 2024 the Parish Union of Siuntio announced that the roof of the church is going to be renovated during the same year.

In 1938 the parish decided to restore the old paintings but sadly they were badly damaged especially on the walls.

A man with all seven deadly sins coming out if his mouth in forms of snakes is depicted on one of the vaults.

[4][2][1] The newer pulpit was donated by president of the Royal Court in Turku, baron Ernst Johan Creutz in 1683.

[1] The baptismal font, made out of limestone, is from medieval era; it was donated to the church by lady Hebbla Siggesdotter Sparre in memory of his husband Councilor of the State, lord Erik Fleming, who owned the Suitia Manor, in 1550.

[1][2][5] There were altogether 34 coats of arms that belonged to different noble houses in the church, but only three remain to this day.

[1][2] The remaining coats of arms are: In 1774 lady Maria Gyllenstierna af Lundholm was granted permission to build a burial chapel out of granite in touch to the church.

When Finland became under rule of the Russian Empire, the Reuterholm family emptied the chapel and left for Sweden.

The painting was donated to the church by Baroness Gyllenstierna af Lundholm in 1773 for payment of the burial chapel.