A small stone Assumption church to be considered in the paper has a unique feature of exterior which is extrinsic to any other religious building in Siberia and in Eastern Siberia in particular. Specific feature of facade decoration of the principle church of the former Nerchinsk monastery of the Holy Dormition is uniqueness of architectural and structural decoration elements of window casings. Window casing decorations of the south facade are different from those ones of the north facade and they are also different from each other. Overall design of window casing decoration is however in keeping with the decoration of Verkhotursk Holy Trinity Church and Irkutsk Epiphany Cathedral, and the author was the first to discover it and gave full reasons in the works. Focus on amazing play of forms and sizes of corbel arches as a basic decoration element of contour architectural appearance of the temple complex contributes to artistic sophistication of the architectural composition.