In order to quickly and accurately measure the fracture toughness of brittle cleavable gallium oxide crystals, to provide a theoretical basis for the precise processing of gallium oxide. A G200 nanoindenter was used to perform a nanoindentation test on gallium oxide crystals. The indentation morphology was analyzed by a scanning electron microscope. The indentation method and the energy method were used to calculate fracture toughness. The fracture toughness of the (010) plane gallium oxide crystal was 0.769 MPa·m1/2, and the fracture toughness of the (010) plane was 0.782 MPa·m1/2. Compared with the traditional fracture toughness testing method, the indentation method and energy method based on nanoindenter can quickly test the fracture toughness of brittle materials with micro damage. Energy method is a more accurate and convenient method for testing nano-scale fracture toughness.