The present work deals with the study of plant ecology of one of most developed wadis of Hijaz mountain in Saudi Arabia namely, wadi Fatimah. Its basin covers an area of 4.860 sq.km extended between 22° 12"", 21° 11"" N and 39° 10"" , 40° 30 E"". The upper part of this wadi consists of the basins of wadis Ash Shamiyah, Al Yamaniyah and Hawrah. After these wadis join, it changes direction abruptly and runs NE then SW across a broad alluvial plain of about 70 km long varies from 2 to 10 km in width. There are no real channels, just a broad flood plain, the wadi here loss its identity and finally reaches the red sea near Al -Hamrah south of Jeddah.