A new simple method of preparation for the thermodynamically unstable octacalcium phosphate [Ca8H2(PO4)6·5H2O; OCP] has been developed using the hydrolysis of α-Ca3(PO4)2 instead of the conventional hydrolysis of CaHPO4·2H2O. The hydrolysis experiments were carried out by treating an α-Ca3(PO4)2(1 g)-H2O(50 m) suspension for 3 h at temperatures in the range 40 to 80° C and at pHs in the range 3 to 7.5. The formation of OCR was limited to within a narrow region between formation regions of other phosphates. Favourable conditions for OCP preparation were, for example, 70° C, pH4.5 to 5.0 and 60° C, pH5.0. Particles of OCP were composed of tight aggregates of strip-like microcrystals growing probably along the [0 0 1] and (1 0 0) plane of the OCP structure. Nearly stoichiometric OCP was obtained under the most suitable conditions with good reproducibility. Pyrolytic processes of OCP were approximately consistent with the data published so far. However, the temperatures of the appearance and disappearance of pyrolytic crystalline phases and ionic species deviated slightly from the published data. Thermal dehydration up to 150° C without destruction of OCP and decomposition reactions above 300° C resulted in changes in surface area and average pore radius of OCP.