Deep levels of undoped GaTe and indium-doped GaTe crystals are reported for samples grown by the vertical Bridgman technique. Schottky diodes of GaTe and GaTe:In have been fabricated and characterized using current-voltage, capacitance-voltage, and deep-level transient spectroscopy(DLTS). Three deep levels at 0.40, 0.59, and 0.67 eV above the valence band were found in undoped GaTe crystals. The level at 0.40 eV is associated with the complex consisting of galliumvacancy and gallium interstitial (VGa-Gai), the level at 0.59 eV is identified as the tellurium-on-gallium antisite (TeGa), and the last one is tentatively assigned to be the doubly ionized galliumvacancy(V∗Ga). Indium isoelectronic doping is found to have noticeable impacts on reducing the Schottky saturation current and suppressing the densities of TeGa and V∗Ga defects. The peak which dominated the DLTS spectrum of GaTe:In is assigned to be the defect complex consisting of VGa and indium interstitial (Ini). Low-temperature photoluminescence(PL)spectroscopy measurements were performed on GaTe and GaTe:In crystals. A shallow acceptor level at 140 meV corresponding to VGa was measured in undoped GaTe. Two shallow acceptor levels at 123 and 74 meV corresponding to VGa and indium-on-gallium antisite InGa were observed in GaTe:In samples. The PL results suggested that the indium atoms could occupy gallium vacant sites during GaTe crystal growth period and thereby change the electrical and optical properties of GaTe crystal.