This paper deals with the effect of thickness of glass material which covered on double slope solar desalination still, performance of the solar still affected by thickness of the glass, which result in to major heat losses in the system. Two inward double slope desalination still with different glass thickness were designed, constructed and experimentally tested their performance. The glasses are inclined 200 from the center of the still. The solar energy collecting area of still is 1m2.The result shows that the variation in glass thickness will affect the efficiency of the still, desalination still with 4mm thickness gives 48% higher fresh water productivity compare to 6mm glass thickness.