In this paper, Hardness, Chemical Resistance and Void Content of hybrid composites with and without alkali treatments were studied. Variation of the above mentioned mechanical properties and chemical resistance were studied with different Cow dung percentage of weight at 5%, 7%, and 10% at constant glass fiber reinforced into the polyester matrix. It is observed that mechanical properties were optimally improved at 7% when compared with 5% and 10 % weight of Fiber. Chemical resistance was also significantly improved for all chemicals except sodium carbonates and toluene. It was observed that the Void content% is reduced in treated composite when compare with the untreated composite. The effect of alkali treatment on the bonding between cow dung/glass composites was also studied. Scanning electron microscope (SEM) were also conducted on the cross sections of fractured surfaces in order to rate the performance hybrid composites were also identified.