Background: Radical gastrectomy followed by adjuvant chemotherapy for advanced gastric cancer brings about serious nutritional impairment. Recent studies have shown an association between body mass index (BMI) and perioperative outcomes of gastric cancer. However, little is known about the association between BMI and long-term outcomes of advanced gastric cancer. Our study evaluated the clinical impact of BMI on the long-term outcomes of gastric cancer staged at II and III, treated by radical gastrectomy followed by adjuvant chemotherapy. Methods: We analysed a total of 211 cases of advanced gastric cancer stage II and III between January 2005 and December 2010 at Chung-Ang University Hospital. The patients were divided into 4 groups according to BMI; underweight, normal, overweight, and obese. In addition, they were divided into two groups (BMI-High vs BMI-Low). We assessed age, sex, tumor location, lymph node involvement, operation method, initial cancer stage, recurrence, and survival (overall survival and disease free survival) between two groups. Results: We classified them into 4 groups according to BMI; underweight, normal, overweight, and obese. There was no difference in overall survival between normal, overweight, and obese group. However, there was significant difference between underweight group and the other groups. As for disease free survival, similar findings were observed. Among 211 patients, 154 patients (72.9%) were included in BMI-L (body mass index < 25), whereas 57 patients (27.1%) in BMI-H (body mass index ≥ 25). There was no difference in age, sex, tumor location, stage, lymph node involvement, operation method, recurrence, and cancer-related death between two groups. When classified into 4 groups as stage II in BMI-H, stage II in BMI-L, stage III in BMI-H, and stage III in BMI-L, overall survival showed significant difference in stage, however, no difference between BMI-H and BMI-L. Disease free survival showed no significant difference in stage and BMI, especially, no significant difference between stage II in BMI-L and stage III in BMI –H. Conclusions: Our findings suggest that preoperative BMI may predict the long term outcomes of advanced gastric cancer after radical surgery and chemotherapy.