In the present article, we report the results of phase I/II combination chemotherapy study of biweekly paclitaxel and S-1 administration in patients with advanced gastric cancer. In the phase I study, we could determine the recommended dose for the phase II study with paclitaxel and S-1 to be 120 mg/m2 and 80 mg/m2, respectively. The side effect was not so severe. The overall response was 53%. In conclusion, biweekly paclitaxel and S-1 administration can be safely combined for the treatment of advanced gastric cancer. This combined therapy represents a novel and active treatment regimen with low toxicity and can be defined as safe and effective. Now we are analyzing the result of the phase II study.