Nutritional parameters may predict the prognosis of patients with gastric cancer. This study investigated whether changes in nutritional parameters before and after chemotherapy were associated with survival among patients who underwent gastrectomy for gastric cancer. We retrospectively reviewed data from 77 Chinese patients who had undergone gastrectomy for stage III gastric cancer at a single center. Laboratory data from before and after chemotherapy were collected regarding peripheral albumin, prealbumin, total protein, hemoglobin, and total cholesterol concentrations. The prognostic nutritional index (PNI) values were calculated and compared before and after chemotherapy. The relationships between survival and the pre-chemotherapy and post-chemotherapy nutritional statuses were evaluated. Among the 77 patients, survival was associated with the staging, the pre-chemotherapy PNI values, and the postchemotherapy body mass index (BMI) values. Significantly better overall survival was associated with a high pre-chemotherapy PNI value (hazard ratio [HR]: 0.485, 95% confidence interval (CI): 0.255-0.920) and a normal post-chemotherapy BMI value (HR: 0.475, 95% CI: 0.249-0.907). Even better survival was associated with the co-existence of a high pre-chemotherapy PNI value and a normal post-chemotherapy BMI value (vs. one or more abnormal parameter, HR: 0.337, 95% CI: 0.167-0.679). Chinese patients who underwent gastrectomy for gastric cancer had nutritional statuses that deteriorated after adjuvant chemotherapy. High prechemotherapy PNI values and normal post-chemotherapy BMI values were associated with better survival outcomes. Thus, low pre-chemotherapy PNI values and/or low post-chemotherapy BMI values may predict poor outcomes among these patients.