Limited energy resources and the need to conserve it, make the optimum and proper design of buildings in terms of energy consumption, indispensable. The type of climate in which the building is constructed in, will also decrease or increase the necessity of this attention. The objective of this study is to evaluate the effect of the window angle on the indoors Mean Radiant Temperature. For this purpose, in the present study, hot and dry climate as one of high priority in regard of energy consumption, has been selected so as to determine the right angle which will reduce the energy consumption by comparing the angle of the window and its effect on the mean radiant temperature. To achieve this goal, the South facade which receives the most exposure over the years, was selected. The daily average Mean Radiant Temperature for the whole year, simulated in ten different angle, in Energy PLus software, was calculated. According to the role in which we expect of window in summer (means avoiding exposure), and winter (means transferring radiation to the inside of the building), and with compering the results for summer and winter, angle of 75 to 80 degrees has selected as the best angle for the whole year.