The purpose of this study was to examine the effects of hypobaric hypoxia on testis morphology and the effects of erdosteine on testis tissue. Caspase-3 and hypoxia-inducible factor 1 expressions were detected by immunohistochemistry. Adult male Wistar rats were placed in a hypobaric hypoxic chamber. Rats in the erdosteine group were exposed to the same conditions and treated orally with erdosteine (20mgkg(-1) daily) at the same time from the first day of hypoxic exposure for 2weeks. The normoxia group was evaluated as the control. The hypoxia group showed decreased height of spermatogenic epithelium in some seminiferous tubules, vacuolisation in spermatogenic epithelial cells, deterioration and gaps in the basal membrane and an increase in blood vessels in the interstitial area. The erdosteine group showed amelioration of both epithelial cell vacuolisation and basal membrane deterioration. Numbers of hypoxia-inducible factor 1-immunostained Sertoli and Leydig cells were significantly higher in the hypoxia group than in the erdosteine group. The number of seminiferous tubules with caspase-3-immunostained germ cells was highest in the hypoxia group and decreased in the erdosteine and normoxia groups respectively. Based on these observations, erdosteine protects testis tissue from hypoxic injury by reducing apoptotic cell death.