The aim of this research was study the effect of dust deposition on solar radiation and solar photovoltaic panel. A theoretical calculation was done and experiments were carried out at Mariout Research Station, El- Amria –Alexandria- Desert Research Center. To study the effect of dust deposition two square plates of glass (20x20 cm) and three pyrnometers were used, the first plate (the control) was cleaned daily and the other was used to determine the solar radiation. The period of the experiment is 175 days from 14^th march to 26^th August 2017. From the experiments; the dust deposition reduces the amount of solar radiation which is falling on the solar panel and creates shadow effect. With the passage of time the density of dust on the panel increases. And this reduces the electric power of the solar panel,. From the data, there was power reduction up to 51.12 %. The efficiency of the solar photovoltaic panel system was reduced from 15.9 to 7.88 % for clean and unclean modules respectively. The total correction solar radiations for the experimental period are 37.4 and 18.28 (kW.h/m²) for clean and unclean modules respectively. The unclean module with dust deposition, showed total output power (24.88%) less than the clean module for the period of 25 weeks.