The Hybrid composites of unsaturated polyester based sisal/glass fibre Hybrid composites were prepared. Sisal is a natural fibre and Glass fibre is a synthetic fibre. These two natural and synthetic fibres are combined in the same matrix (unsaturated polyester) to make Sisal/Glass fibre Hybrid composites and the Compressive and Impact properties of these hybrid compositeswere studied.Asignificant improvement in Compressive and Impact properties of Sisal/Glass fibre Hybrid composites has been found. The Chalk powder (additive) is also added to the resin (unsaturated polyester) in proportions of 1%,2%,3%byweight of resin respectively and Sisal/Glass fibre Hybrid composites were prepared by using this resin to study the effect of Chalk powder on Compressive and Impact properties of these hybrid composites. It is also observed that as the Chalk powder quantity increases Compressive and Impact properties are decrease.