Persian architecture emphasized on Beauty, and by means of Sacred Geometry Persians measured the proportions of heaven and reflected them in the dimensions of buildings on the earth. By using mathematics, Iranian architecture has achieved a high level of beauty and perfection. Geometry was used not only to solve structural problems, but also in the details of the designs of various structures. Despite its extraordinary richness, Islamic architecture has rarely been studied for its conceptual and symbolic significance. All the elements of the Islamic architecture of Persia from the simplest architectural unit to a complex urban environment are woven around this central doctrine and thus are best understood as multiple manifestations of unity. This paper first will introduce Islamic geometrical patterns, say something about their characteristics and origins and point the reader to a variety of resources on Islamic Patterns. Second it will be explained about the use of the science of geometry in design of a number of Persian historical buildings. The geometric factors upon which the design of these buildings, from both architectural and structural viewpoints, is made will be discussed.