125 Background: S-1 adjuvant chemotherapy improves survival of stage II/III gastric cancer, however, the compliance is not high. The aim of the present study is to clarify risk factors for continuation of S-1 after gastrectomy. Methods: Patients were retrospectively selected according to the following criteria; (1) patients underwent curative D2 gastrectomy for gastric cancer during 2002 and 2010, (2) pathological stage II/III, (3) creatinine clearance more than 60 ml/min, and (4) S-1 was initiated at a dose of 80mg/m2 within 6 weeks after surgery. Clinical factors when starting S-1 chemotherapy were examined by uni- and multi-variate analyses. Results: Seventy-five patients were eligible. Median age was 62 years (range: 36-80). Performance status was 0 in 65 patients and 1 in 10. Serum albumin level was >4.0 g/dl in 34 patients and <4.0 g/dl in 39. Operative procedure was total gastrectomy (TG) in 46 patients and distal one in 29. Median percentile of body weight loss to preoperative state (%BW loss) was 9.3 (range 0-21.1). Stage was II in 22 patients and III in 53. When %BW loss was classified to two groups; LOW (<15%, n=64) and HIGH (>15%, n=11), S-1 continuation rates were 82.8% in the LOW and 54.6% in the HIGH at 3 months and 73.2% in the LOW and 45.5% in the HIGH at 6 months, which were statistically significant (p=0.025). Among age, performance status, type of gastrectomy, %BW loss, serum albumin, and stage, only %BW loss was a significant independent risk factor for S-1continuation with hazard ratio of 2.437 by multi-variate Cox proportional hazard analyses (p=0.039). Conclusions: To improve drug compliance which leads to survival, it is a key to maintain BW before starting adjuvant chemotherapy. Peri-operative nutritional therapy should be developed and be focused on chronic inflammatory phase after surgery and on starvation after gastrectomy. A randomized phase III trial is on-going to show efficacy of peri-operative nutritional support including eicosapentaenoic acid (EPA).