The mechanical properties viz.impact strength and tensile modulus of polypropylene (PP) containing two different types of calcium sulphate (prepared by in situ method under controlled conditions in a polymer matrix i.e. polyethylene oxide in the composition range 0-25 wt% of filler were studied. Increase of impact strength together with high crystallinity and improved tensile modulus was observed in one of the grades of CaSO4 filled composite as compared to pure PP. This could be associated with the long needle shaped CaSO4 crystals and the change in the structure and morphology induced by the same in the PP matrix.