GaSb is the most suitable substrate in the epitaxial growth of mixed semiconductors of GaSb system. In this work, Te-doped GaSb bulk crystals with different doping concentration have been annealed at 550 °C for 100 h in ambient antimony. The annealed samples have been studied by Hall effect measurement, infrared (IR) optical transmission, Glow discharge mass spectroscopy (GDMS) and photoluminescence (PL) spectroscopy. After annealing, Te-doped GaSb samples exhibit a decrease of carrier concentration and increase of mobility, along with an improvement of below gap IR transmission. Native acceptor related electrical compensation analysis suggests a formation of donor defect with deeper energy level. The mechanism of the variation of the defect and its influence on the material properties are discussed.