Abstract: The main issue of desiccant cooling system is less COP in compared with conventional cooling system. This issue is due to effect of component effectiveness and operation condition of desiccant cooling system. This study presents the effects of significant parameters (effectiveness of components and operation parameters, namely, regeneration temperature, airflow rate, rotational speed, solar system and outdoor condition) on the performance of evaporative and hybrid desiccant cooling systems in different climates. It was achieved that performance can be increased by reducing regeneration temperature and air flow rate, increasing the number of solar collectors and increasing the outdoor temperature and humidity. The optimal desiccant wheel rotation speed should be within the range of 5-10 r h–1.