One of the hallmarks of the current era is the overlap and interaction among sciences, and the exploitation of the various scientific developments in expanding the knowledge base. Recent years have witnessed increasing interest in a number of mathematical and computer sciences, one of these sciences is the fractal geometry. This geometry has evolved into the engineering applications at an accelerated pace, and its applications included the different fields of science and engineering. It is found that there is a close relationship between the fractal geometry and some basic concepts in architecture. The fractal geometry gives a special vision which is useful for understanding and analysis of ancient and modern buildings in architecture. This paper deals with two basic properties in fractal... geometry, namely the property of self-similarity and fractal dimension. These two properties are studied on a number of mosques in Islamic architecture for the purpose of numerical measuring of the self-similarity property. The samples of this study are chosen from the Ottoman mosques in Islamic architecture, and studied and analyzed by using a computer program which was developed specifically for this study. The most important conclusion in this research is Islamic architecture has the property of self-similarity, which is an essential feature in Islamic architecture.