The heating properties were investigated for Al₄SiC₄ powders with various particle sizes (3.0 μm to 1-2 mm) to develop 2.45GHz microwave well absorber. The single-mode cavity, which is able to separate electric field heating and magnetic field heating, was employed as microwave heating systems and the heating behavior was investigated at separated electrical field employing a radiation thermometer. Their electrical permittivity for 2.45GHz were measured by the cavity perturbation method. Al₄SiC₄ were compared with Al₂O₃ in both heating behavior and electrical permittivity. The microwave absorption of Al₄SiC₄ powders increases with their grain size, 1-2 mm particles powders indicates higher temperature than 3 μm in their microwave heating.