AbstractOyster shell powder was used as the admixture of ordinary portland cement. The effects of different addition amounts and grinding ways on the strength and stability of cement mortar were discussed and proper addition amount of oyster shell powder was determined. The structure and property changes of cementing samples with different oyster shell powder contents were tested by XRD and SEM means. The results revealed that compressive and rupture strengths of the sample with 10% oyster shell powder was close to those of the original one without addition. Stability experiment showed that the sample prepared by pat method had smooth surface without crack and significant expansion or shrinkage after pre-curing and boiling, which indicated that cementing material dosed with oyster shell powder had fine stability. XRD and SEM observation showed that oyster shell independently exists in the cementing material.