This study was proceeded to adjudge a hybrid solar drying system for drying onion slices. Experimental work was proceeded under different levels of air temperature “50, 60 and 70°C", and thickness of onion slices “2, 4 and 6 mm" at constant air velocity of 0.32 m/s. The experimental measurements included onion slices moisture content, air temperature, solar energy flux incident, thermal drying efficiency and quality changes of the dried onion. Two different drying models “Lewis' model and Henderson and Pabis's model" were also mathematically analyzed to describe the drying behavior. The results show that, the solar collector of the dryer could increase the air temperature inside the plenum chamber by 7.58 to 8.46 °C. The reduction in onion moisture content increased by increasing of air temperature and decreasing of slice thickness. The overall thermal efficiency of the tested dryer ranged from 22.9 to 34.7% and the solar collector provided “87.74, 78.83 and 67.46 %" of the total heat energy consumption to raise up the air temperature to the levels of “50, 60 and 70 °C", respectively. Both examined models could describe the drying behavior of onion slices satisfactorily, but Lewis' model was more precise. Quality evaluation tests showed that the rehydration ratio ranged from 3.95 to 5.53 for the treated onion and from 4.37 to 5.6 for the un-treated samples. Also the treated samples showed higher thiosulphinate content than the un-treated samples. While the increase in drying temperature and slice thickness resulted in higher reduction of ascorbic acid content.