Porous granules of β-tricalcium phosphate (β-Ca3(PO4)2; β-TCP) were prepared from porous hydroxyapatite granules with calcium deficient composition synthesized by hydrothermal method. The β-TCP granules were composed of rod-shaped particles of about 10-20 µm in length. Rod-shaped particles were locked together to make micro-pores, and the size of micro-pores formed by tangling of rod-shaped particles was about 0.1-0.5 µm. The granule size, particle size, and micro-pore size could be controlled by our unique method. The porous granules of β-TCP must be suitable for the bone graft material and for scaffold of cultured bone.