Crystallized apatite behaved to plaster of Paris was prepared by the chemical method. Apatite powder was mixed with chitosan. In this study, it was also studied the effect of HA seed and sodium hydrogen phosphate as an additive on their mechanical strength, compared with the normal calcium phosphate cements. Setting time of paste cements was determined using Gillmore method. Phases of cement obtained from a crushed cylinder were analyzed using XRD analysis. From the results, chitosan was effective both in increasing mechanical properties and accelerating hardening of the normal bone cements. Nevertheless, the compressive strength of chitosan-crystallized apatite composites was not significantly improved as compared to the controlled one. In addition, it was found that the mechanical strength of the cements decreased when increasing the concentration of HA seed and an additive.