Biphasic ceramic consisting of tricalcium phosphate with α- and β -phases (αβ-TCP) is a candidate as biodegradable bone substitutes since its biodegradability may be controlled by the ratio of the phases. In the present study, preparation of porous αβ-TCP body with continuous pores of 10-50 µm in diameter was attempted using additives of Mg, and its in vivo behavior was examined. Powder of β-TCP was mixed with Mg and potato starch to form slurry, followed by loading in polyurethane foam. The sample was fired at 1400°C for 12 hours for sintering process. α-TCP content of the sample decreased with increasing the Mg content, while β-TCP increased. Ceramic body consisting of β-TCP phase was obtained when 1.0 mass% of Mg was added. Porosity of the body decreased with increasing the content of Mg. The αβ-TCP body with 80% porosity was obtained when the content of Mg was 0.1 mass%. The in vivo experiments showed that the rate of degradation of the obtained αβ-TCP was almost same as α-TCP, and much higher than β-TCP.