Campus outdoor urban spaces consider effective spaces for students to take a walk or engage in recreation and social activities or studying. A comfortable thermal environment is extremely important for students to enjoy the outdoor urban spaces. Wherefore thermal comfort in urban spaces is a crucial issue, but the warmer urban climate may have some negative impacts on outdoor thermal comfort of student in campus. Therefore, the aim of this study was to investigate the effect of aspect ratio of urban space, which is one of most effective strategy to improvement outdoor thermal comfort. ENVI-met numerical simulation applied to examine a series of aspect ratio scenarios. ENVI-met run for main entrance space in BUE campus, Cairo, Egypt. The effects of aspect ratio on outdoor thermal comfort dealt with in detail. The results show that aspect ratio (H/W=3) could be considered starting point to respect outdoor thermal comfort.