As a primary medium of decoration, brick was also used as the main structural material in the early Islamic buildings in Iran. The advancement in construction and innovation of glazed bricks led to development of brickwork decorations during the Seljuq dynasty in Iran and a variety of design were created in brickwork decorations and applied in most of the buildings of this period. Since brickwork decorations were constructed by arranging vertical, horizontal, and oblique of small pieces of bricks, the final patterns appears as plaid textures on the buildings. However, taking into account their substructure, a sort of geometric construction could have been proposed for their design. Based on the aforementioned hypothesis, some examples of brickwork decorations from Iranian Islamic architecture have been analyzed in this paper. The analyses are carried out by considering the whole ornamental patterns in order to extract assumed methods and geometric divisions for their substructure.