PURPOSE: Varicocele is known as a main cause of primary male infertility and it supposed to be associated with oxidative stress. Anthocyanin is known as a natural plant pigment and novel antioxidant. This study was designed to investigate the effects of anthocyanin on a rat model of varicocele. MATERIALS AND METHODS: Twenty four male rats, induced varicocele by partial obstruction of left renal vein, were divided into four experimental groups: the group induced varicocele for four weeks without anthocyanin, the group received anthocyanin (80 mg/kg) right after varicocele induction, group induced varicocele for eight weeks without anthocyanin, and the group received anthocyanin (80 mg/kg) after four weeks observation following varicocele induction. After anthocyanin treatment, testes from the rats in all groups were removed, weighed, and subjected to histological examination. Apoptosis in the testes was measured by the TUNEL assay. And the oxidative stress was evaluated by measurement of 8-hydroxy-2'-deoxyguanosine (8-OHdG). RESULTS: Induction of varicocele led to decreasing left testis weight, decreasing spermatogenic cell density significantly (p<0.05). Also it led to increasing apoptotic body counts and increasing concentration of 8-OHdG significantly (p<0.05). However administration of anthocyanin right after varicocele induction prevent this change meaningfully (p<0.05). In group received anthocyanin after four weeks observation following varicocele induction, interestingly, there was no significant difference in testis weight, spermatogenic cell density, apoptotic body count and concentration of 8-OHdG compared to group induced varicocele for eight weeks without anthocyanin administration. CONCLUSIONS: These results suggest that anthocyanin is effective in decreasing the oxidative stress of testis in rat induced varicocele and may be effective in making a healthy sperm in patient of varicocele in early stage. However in patient under way in advanced stage, it is supposed that the anthocyanin cannot help having a protective effect from oxidative stress narrowly unless the condition of oxidative stress by varicocele is corrected. Further studies are needed to better understand the mechanisms and actions of anthocyanin and varicocele, and these studies may lead to the clinical application of anthocyanin in preventing male infertility by varicocele.