Influence of powder characteristics such as specific surface area, agglomerate size and shape, on their microstructures and mechanical properties of green and sintered bodies was studied for seven kinds of calcium hydroxyapatites. A heat treatment above 1300°C gave tricalciumphosphate (TCP) for all powders. Before the formation of TCP, decarbonation took place in carbonate-containing powders above 800°C, while carbonate-free powders were stable up to 1200°C. Powders with high specific surface areas (SSA), especially larger than 40m²/g, had good sinterabilities, and gave dense bodies about 99% relative density after a heat treatment at 1200°C. On the contrary, powders with lower SSA, about 10m²/g, had poor sinterabilities and gave porous bodies. Poor sinterability was mainly ascribed to the stability and needle like shape of the crystallites. Furthermore, presence of large voids among the agglomerates prevented densification of the compacts at the late stage of sintering. The high density Ca-HAP ceramics prepared in this report have mechanical properties comparable with those reported in the literatures.