In this paper, I examined two church types which included in Sebastiano Serlio's Fourth Book on architecture and clarified their composing method by using some squares which are related to the'width of their fagades. The results are as follow ; The method of constructing a porta is used for decide diameter of column in these church facades. The square which length of sides are 24 diameters of column (or widths of pilaster) is fundamental for these church facades, and it is used for decide the whole form of the facade. The geometrical scheme of constructing a porta which is included in Serlio's First Book is one of his architectural design methods.
