Calcium phosphate was prepared by chemical reaction formula using Oyster shells and H 3 PO 4 solutions. After added to 0.1 M∼0.9 MH 3 PO 4 solution for oyster shell, prepared powders were investigated for heating properties and formation phase with heat treatment temperatures. As the results of XRD analysis of heated powders at 500 ? C ∼ 1200 ? C , CaCO 3 phases were observed at the temperature of below 900 TEX> ? C and in the condition of 0.1 M∼0.9 M H 3 PO 4 solutions. However, CaCO 3 , CaPO 3 (OH) and Ca 3 ( PO 4 ) 2 phases were appeared at the temperature range between 500∼900 ? C and in the solution of 0.7 M to 0.9 M H 3 PO 4 . Ca 5 ( PO 4 ) 3 (OH) and CaO phases due to the decarbonation of oyster shells( CaCO 3 ) were appeared at above 1000 ? C and in the solution of below 0.5 M H 3 X PO 4 . However in the case of above 0.7 M H 3 H 4 solutions, Ca 5 ( PO 4 ) 3 (OH) was decomposed into Ca 3 ( PO 4 ) 2 at more higher 100 0 ? C . Thus Ca 3 (X Ca 4 ) 2 phases were appeared at higher than 100 0 ? C .