Effect of aluminum ion on synthesis of precipitated calcium carbonate by carbonation process was investigated with changing its amount of addition, mixing condition and reaction temperature. 0.2 mole $Ca(OH)_2$ was added to 2L of 0.1M $NaAlO_2$ aqueous solution, and then calcium carbonate was synthesized by blowing $CO_2$ gas into the suspension. For Ca/Al>1(molar ratio), only calcite powder was precipitated, for Ca/Al=1, both calcite and aragonite were precipitated and for Ca/Al<1, the content of aragonite decreased. The raising of reaction temperature made the pH of the suspension lowered, and it resulted in progress of formation of aragonite phase at $80^{circ}C$.