Objective: The aim of this study was to evaluate the effect of pentoxifylline (PF) on the conventional ICSI program undergone in severe asthenozoospermia. Method: Total 348 cycles of ICSI programs undertaken at CHA General Hospital from January, 1996 to September, 2000, were divided into two groups - injected with pentoxifylline-treated sperm (PFT, 204 cycles) or non-treated sperm (NPFT, 144 cycles) and the clinical results of PFT group were compared with those of NPFT. Results: PF-treatment on sperm increased their motility of normozoospermia and severe asthenozoospermia. Fertilization rate of PFT group was higher than those of ICSI programs undertaken using sperm of NPFT (70.6% vs. 62.9%, p<0.01). And, ET and clinical pregnancy rates of PFT were slightly higher than those of NPFT (93.1%, 44.2% vs. 90.3%, 36.2%). Conclusion: These results showed that treatment of pentoxifylline has a beneficial role on selection of viable sperm in severe asthenozoospermia.