Internal courtyard played a vital role in the architecture of many civilizations in various countries, centuries and building's kinds. It was a major element in the architecture of MASJID in a variety of natural environmental conditions for nearly thousand years, then gradually disappeared nowadays. So the aim of this theoretical and practical study, is to present the importance of the internal courtyard's DAYLIGHTING for the environmental architecture of MASJID in the city of Cairo,  to raise the values of DAYLIGHTING's factor and intensity, with the quality of its distribution inside the space around the day, in addition to its role in meeting the human needs of ventilation, thermal comfort, de-noising, availability of sky and hosting various religious, cultural and social activities, which support the ecosystem. On the other hand, clerestory, dome, exterior windows, and artificial lighting do not meet the functional needs, and they increase energy consumption, in addition to their psychological and social negative impacts, which increase the pollution loads on the environment. So we have to support the internal courtyard in architecture, using suitable technology to take advantages of DAYLIGHTING and the natural resources for supporting the ecosystem