The layer-structured thermoelectric material, Al-doped (ZnO)₅In₂O₃, was fabricated by microwave irradiation within a short time of 15 min and its thermoelectric properties were examined. When comparing specimens sintered by microwave irradiation (15 min) with those by conventional heating (4 h), their microstructure and composition were similar. However, electrical conductivity was improved by microwave irradiation. Moreover, in (Zn_1−xAl_xO)₅In₂O₃ (x = 0.016, 0.032), Al-doping contributed to an increase in both the electrical conductivity and the absolute value of Seebeck coefficient, which contributed fairly to the high dimensionless figure of merit, ZT. Larger ZT was achieved by improvement in electrical conductivity by microwave irradiation and increases in both the electrical conductivity and the absolute value of Seebeck coefficient by Al doping. (Zn_0.984Al_0.016O)₅In₂O₃ sintered by microwave irradiation had the highest ZT, which was 1.5 times higher than that of (ZnO)₅In₂O₃ sintered by conventional heating at 773 K.