We used combination therapy of S-1 and Paclitaxel to treat gastric cancer complicated by carcinomatous ascites and assessed the clinical results. The subjects were 8 patients who were gastric-cancer-ascites-positive, and they were treated by biweekly administration of S-1 orally, continuously for 2 weeks, and Paclitaxel on day 1 and day 8 of S-1 administration. The results showed disappearance of the ascites on diagnostic images in 37.5% (3/8) and PR in 50% (4/8) in terms of the main gastric cancer focus. An average 15 courses were conducted, and the overall adverse event rate was 87.5% (7/8). Hematologic toxicity occurred in 75.0% (6/8), and it was G3 or 4 in 37.5% (3/8). Non-hematological toxicity was confirmed in 75.0% (6/8), but none of it was G3 or 4. Although they were historical controls, we assessed the results of treatment in a conventional treatment group (control group; n=24) and the S-1 and Paclitaxel group (S-1+Paclitaxel group; n=8) by comparing the survival rates. MST in the S-1 and Paclitaxel group was 413 days, and the longest survival time was 1,148 days. The 1-year survival rate was 62.5%, and the 2-year survival rate was 37.5%. The survival rate in the S-1+Paclitaxel group was better than in the control group (p<0.001). We have reported this study because S-1+Paclitaxel therapy appears to be an important method of treating gastric cancer complicated by carcinomatous ascites.