This study aims to investigate the ability of improving the properties of lightweight cement mortar containing limestone and pumice stone treated with sodium hypochlorite (NaOCL). Treated limestone and treated pumice were used as fine aggregate in cement mortar mixtures. Control cement mortar using untreated limestone and untreated pumice were also prepared for comparison purpose. The effect of sodium hypochlorite on some physical and mechanical properties of limestone and pumice were also investigated. Compressive strength of cement mortar was examined at ages of 3, 7 and 28 days. Results demonstrated that the treated limestone and treated pumice increased cement mortar strength significantly. The cement mortar containing treated pumice showed high strength as compared with cement mortar containing treated limestone. The results also indicated that sodium hypochlorite improve limestone and pumice stone characteristics as a mean of specific gravity, absorption, abrasion resistance and compressive strength.