Reports of the results of clinical trials on adjuvant chemotherapy for curatively resected gastric cancer in Japan and other countries were reviewed. The efficacy of adjuvant chemotherapy outside Japan was not recognized except in two trials. Japanese trials did not reveal a significant survival benefit compared with surgery alone. However, a consensus was achieved in Japan on its efficacy by understanding some results of subset analysis as definite proof. Recently, it has been recognized that the re-evaluation of adjuvant chemotherapy should be carried out with the control group of surgery alone. The results of the trials of JCOG and N.SAS-GC, comparing adjuvant chemotherapy versus surgery alone, are much awaited. At the present time, carefully designed randomized controlled trials with sufficient sample size, which include surgery alone for control arm, are the only way to establish the efficacy of adjuvant chemotherapy.