Thermal comfort in outdoor spaces is a crucial criterion for evaluating the quality of environments with outdoor activities.Throughout history,architects have always paid attention to it. To achieve thermal comfort, considering the climate is essential, as clearly evident in traditional Iranian buildings.Among these, traditional mosques, due to their religious significance and the continuous use of their outdoor spaces, have been of greater importance. Architects have provided the best responses to the climate to achieve thermal comfort.Therefore, the aim of this research was to investigate the optimal height-to-width ratios and the optimal area of open spaces in traditional mosques in Greater Khorasan.By utilizing the results, an optimal model for contemporary mosques in Greater Khorasan was presented.The research area, Greater Khorasan, regardless of current spatial boundaries, included four different climatic zones, with the cities of Quchan, Mashhad, Sabzevar,and Tabas as case studies. In the research process, the impact of height-to-width ratios and the area of open spaces on thermal comfort during the noon prayer in the summer season was investigated.After a qualitative review of the existing literature and theoretical foundations, thermal comfort in the enclosed space was numerically analyzed by simulation in the ENVI-MET4 and analysis of the simulation results in Leonardo based on the PMV index.The results of the research indicate that the optimal percentage of the courtyard in the four climatic zones is 40%.The optimal proportions for the city of Quchan are H'/W=1, H=8, H'=10, H/W=0.8, for Mashhad H=H'=14, H/W=1.4, H'/W'=1,for Sabzevar H=H'=14, H/W=1.4, H'/W'=1, and for Tabas H=H'=14, H/W=1.4, H'/W'=1.