Positron annihilation spectroscopy(PAS)and photoluminescence (PL) have been adopted to study defects in proton-irradiatied Zn-doped GaSb. A monovacancy VGa having a lifetime of 293 ps was observed in the non-irradiated sampls and a divacancy VGaVSb with a tifetime of 333 ps was identified in the proton-irradiated samples when the fluence reached 3×1015 cm-2.The PL results reveal that the acceptor Zn is not related with proton irradiation-induced defects, which act as non-radiation recombination centers in the samples. The acceptor level of Zn in GaSb has been calculated from the PL spectra. After proton irradiation, interstitial monatomic hydrogen in a negative charge state (Hi-) in GaSb has been found, which acts as a shallow-acceptor. Annealing experiments indicated that the as-grown and proton-irradiated samples have different annealing behaviors, the reason for which was attributed to the existence of monatomic hydrogen interstitials in the proton-irradiated samples.