Rainfall simulation is an easy and relatively cheap method to get remarkable amount of hydrological data within short period of time instead of depending on a very rare natural rainfall particularly in arid regions. This technique was largely utilized in different parts of the worlds especially in arid and semiarid regions. However, research and applications of rainfall simulators are very rare in the Arab World. This study is probably one of the earliest applications of rainfall simulators in this part of the world. The study location is an experimental plot within the main stream of Namman basin located in the south east of Makkah city in western Saudi Arabia.  In this study, six rainfall simulation experiments are conducted using rainfall simulator which has been developed from locally available materials.  The experiments provided values of runoff and infiltration volumes resulted from simulated rainfall events which have varied characteristics. The results of the study indicated that values of runoff volume mainly depend on values of rainfall intensity and then on values of rainfall duration. The results of the study are promising and it is recommended to conduct more rainfall simulation experiments on the study region and on other semi arid regions in the Arab World.