To prove the efficacy of adjuvant therapy for curatively resected advanced gastric cancer, large-scale randomized control trials are necessary based on the idea of EBM (Evidence Based Medicine). We had a long history of adjuvant therapy and many trials were conducted so far. However, many problems were also pointed out in past trials, even in the several trials with positive results. After accumulation of the knowledge of a good clinical trial, we started to organize study groups like JCOG (Japan Oncology Group) for high-quality clinical trials in Japan. The positive result of the National Surgical Adjuvant Study of Gastric Cancer (N. SAS-GC) is encouraging after the long period of negative results from adjuvant trials. This trial was well designed randomized clinical trial (RCT) with statistically significant difference of survivals,which suggest the efficacy of the adjuvant chemotherapy with UFT. However, because of the reduced sample size of this trial, we need one more trial with sufficient sample size to prove the efficacy of adjuvant chemotherapy for gastric cancer as the definitive evidence.