Two novel microwave dielectric materials LiBO2 (B = Ga, In) were synthesized by a solid-state reaction method. The orthorhombic structured LiGaO2 sintered at 1075 °C for 4 h exhibits a relative density of 96.1 ± 0.2 % and dielectric properties, namely, εr ∼ 5.82 ± 0.01 (16.7 ± 0.1 GHz), Q × f = 24,500 ± 2000 GHz, and τf ∼ -74.3 ± 2 ppm/°C. Meanwhile, the tetragonal structured LiInO2 sintered at 920 °C for 4 h exhibits a relative density of 85.3 ± 0.2 % and dielectric properties, namely, εr ∼ 9.6 ± 0.01 (15.2 ± 0.1 GHz), Q × f = 39,600 ± 2000 GHz, and τf ∼ 9.8 ± 2 ppm/°C. The dielectric properties were investigated by chemical bond theory, and results indicate that the τf value is closely related to the bond ionicity. The good chemical compatibility of LiInO2 ceramics with silver electrodes makes it a potential material for LTCC technology.