Kallio Church is richly decorated. The decorative program of the church was designed by its architect Lars Sonck. The floral motifs are strongly stylized in the spirit of Art Nouveau. Roses adorn the window and doorway recesses and merge in the arches with cross and wreath motifs.

The stairways leading to the galleries form a single gilded rose garden, with 736 roses on the eastern side and 724 on the western side. As a Christian symbol, the rose represents Christ as a symbol of love, and the Virgin Mary.