After Adjuvant Chemotherapy Trial of S-1 for Gastric Cancer(ACTS-GC), adjuvant chemotherapy with S-1 is a standard treatment for stage II or III gastric cancer patients. In this study, we retrospectively examined factors that influence the continuity of S-1 adjuvant chemotherapy. We analyzed the clinical documentation of 27 gastric cancer patients being treated with S-1 adjuvant chemotherapy. Patients who completed the treatment without reduction dose were classified into a complete group(n=14), and those for whom S-1 was discontinued or reduced due to adverse reactions were classified into a reduced/discontinuation group(n=13). First, we examined the background factors at baseline between these two groups. Univariate logistic regression analysis revealed that the operative procedure, leukocyte count, and serum creatinine level at baseline were identified as factors that influence the continuity of S-1 chemotherapy. Next, we investigated the hematological and nutritional conditions of these patients during the treatment period. The loss of body mass index(BMI)during the treatment period was remarkable in the reduced/discontinuation group regardless of the operative procedure. This result suggests that an early nutritional intervention might be important for gastric cancer patients undergoing S-1 adjuvant chemotherapy.