Seeking design alternatives that achieve an efficient functional performance in buildings is an essential part of design process and that the provision of these alternatives is one of the greatest challenges that face the architect in solving the designing problem. The buildings of mosques are deemed important parts of Islamic architecture characterized by the fixation of their necessary spaces with time, from previous studies of mosque buildings, the research problem were determined as “ there are insufficiency in the functional performance of design alternatives related to mosque designs and need to make use of optimization process in providing the most efficient substitute in designing mosque” therefore, the research aims at finding a new scientific method (computerizing the design process) to create design alternatives having a high functional efficiency that achieve  maximum benefit from using area of mosque that match with special criteria and preferences to designing the building of the mosque, in order to achieve this goal, the research has been divided into four parts the first includes optimization studies and general Islamic Architecture studies that deal with mosque design and identifying the problem and the aim behind the research. The second including building a theoretical framework that determines design criteria and special space relations of designing floorplan for mosque building in addition to formulation  those criteria and relations into mathematical functions to be constraints in the optimization models, In the third a computer program was developed using optimization models as a mechanism in producing efficient design alternatives and as a tool for applying design criteria and the amount of wasted areas selected samples. The fourth including a mechanism for producing design alternatives and analyzing results through making a comparison between the samples produced by the program and the current floorplan for the building of modern mosque in the city of Mosul to show how efficient the produced alternatives are through this program as compared with current designs