Windows allow the daylight to naturally illuminates the indoor space, save energy for lightings, and create healthy working environment. However, excessive daylight increases the heat gain and causes discomfort glare. Therefore, external screens are used to control daylight. Incorporate ancient design screen such as Mashrabiya will not alter the traditional design of the building. The traditional screen provides natural light, natural ventilation, and privacy. Mashrabiya is a framework consists of a crisscrossed pattern of strips made of building material, such as wood, or Gibson. In this study, experimental measurements have been conducted to study the effect of installing the perforated screen on the indoor illuminance level and heat gain through the window. The temperature and heat flux at the indoor surface of the window are measured in the month of June. The illuminance level in the indoor space, indoor and outdoor air temperatures, and global solar radiation in the site are measured. The window is facing west direction. Several design patterns of the screen were considered. The heat gain is decreased by up to 53%, without significant negative impact on the indoor natural illumination.