Purpose: The prognostic nutritional index (PNI) is considered useful for predicting the prognosis of patients with gastric cancer (GC). This retrospective study investigated the relationship between both the pre- and postoperative PNI and the prognosis of GC patients. Methods: The subjects of this study were 254 patients who underwent curative surgery for histopathologically diagnosed GC. Results: Patients were divided according to their pre- and postoperative PNI as follows: preoperative PNI of ≥ 52 (pre-PNIHigh), preoperative PNI of &lt
 52 (pre-PNILow), postoperative PNI of ≥ 49 (post-PNIHigh), and postoperative PNI of &lt
 49 (pre-PNILow). Both pre- and postoperative PNI were significantly associated with GC prognosis. Patients were then divided as follows: group A, patients with pre-PNIHigh and post-PNIHigh
group B, patients with either pre-PNIHigh and post-PNILow or pre-PNILow and post-PNIHigh
and group C, patients with pre-PNILow and post-PNILow. The 5-year survival rates were 100.0, 83.0, and 67.1% for groups A, B, and C, respectively. Multivariate analysis indicated that the combination of pre- and postoperative PNI was an independent prognostic indicator. Conclusions: Combined analysis of the pre- and postoperative PNI offers accurate information about the prognosis of patients with GC.