Background: It is shown that TS-1 as adjuvant chemotherapy after D2 resection in patients with gastric cancer can improve DFS and OS in one Japanese Trial. And TS-1 has become one of the standard therapies to these patients. But it is still unknown whether it would improve more to OS and DFS than single TS-1 after combined with oxaliplatin . This trial is designed to investigate the efficacy and safety of TS-1 plus oxaliplatin versus TS-1 single as adjuvant chemotherapy after D2 resection in patients with gastric cancer.

Patients and methods: In this study , patients with histologically confirmed gastric cancer who received D2 resection and staged II or III, aged from 18 to 70 years and with Eastern Cooperative Oncology Group performance status ≤2 and adequate organ function, are randomized 1:1 to oxaliplatin 100mg/m2 on day 1 and TS-1 40~60mg twice everyday for 14 days in a 21-days cycle for total 6 cycles followed by TS-1 single with the same dose and frequency to the end of the 1st year postoperatively(SOX) , or TS-1 single 40~60mg twice everyday for 14 days in a 21-days cycle to the end of the 1st year postoperatively (TS-1). The primary end point is overall survival (OS), and secondary end point is disease free survival(DFS) and safety. Final study analysis will be conducted in the end of the 5th year after the last patient's enrollment.

Inclusion Criteria:

• informed consensus of patients
• be able to receive oral administration
• from 18 to 70 years old
• be proven to be primary adenocarcinoma of gastric cancer and staged II or III by pathological evidences
• without other chemotherapy and/or radiation against to the disease
• normal function of other organs including heart,liver ,kidney and so on
• Eastern Cooperative Oncology Group performance status:0~2

Exclusion Criteria:

• history of other malignancy
• allergic reaction to S-1 or oxaliplatin
• be enrolling in other clinical trials
• abnormal GI tract function
• dysfunction of other organs
• female in pregnancy or lactation,or refuse to receive Contraception measures during chemotherapy
• other situation to be judged not adaptive to the study by investigators