This study investigated the protective effects of diallyl disulfide (DADS) against cyclophosphamide (CP)-induced testicular toxicity in male rats. DADS was gavaged to rats once daily for 3 days at 100 mg/kg/day. One hour after the final DADS treatment, the rats were given a single intraperitoneal dose of 150 mg/kg CP. All rats were killed and necropsied on day 56 after CP treatment. Parameters of testicular toxicity included reproductive organ weight, testicular sperm head count, epididymal sperm motility and morphology, epididymal index, and histopathologic examinations. The CP treatment caused a decrease in body weight, testicular sperm head count, epididymal sperm motility, and epididymal index. The histopathological examination revealed various morphological alterations, characterized by degeneration of spermatogonia/spermatocytes, vacuolization, and decreased number of spermatids/spermatocytes in the testis, and cell debris and mild oligospermia in the ductus epididymis. In contrast, DADS pretreatment effectively attenuated the testicular toxicity caused by CP, including decreased sperm head count, epididymal sperm motility, and epididymal index and increased histopathological alterations in the testis and epididymis. These results indicate that DADS attenuates testicular toxicity induced by CP in rats.