The obesity paradox is reported to exist in various diseases. However, obesity is a pivotal issue in gastric cancer (GC) patients because of the surgical difficulty related to postoperative abdominal infectious complications (PAIC). This study clarified the existence of the obesity paradox in GC. Between 1997 and 2015, 1536 consecutive patients underwent curative gastrectomy. Of all patients, 18.6% (285/1536) were obese and tended to have a better prognosis (P= 0.073). In patients without PAIC, obesity was a significant prognostic factor for 5-year overall survival (P= 0.017). PAIC was an independent poor prognostic factor in both obese and non-obese patients (P< 0.001; hazard ratio [HR] 4.22 and 1.82). In pStage II–III patients, there was a large and significant prognostic difference between non-PAIC and PAIC obese patients (P= 0.006; 5-year overall survival: 69.7% vs. 43.8%) related to the higher incidence of peritoneal recurrence in PAIC obese patients (P= 0.035; 31% vs. 10%). Whereas, there was a small prognostic difference between non-PAIC and PAIC non-obese patients (P= 0.102; 5-year overall survival: 56.5% vs. 51.9%). Although the obesity paradox is present in GC, PAIC had a more negative prognostic impact through peritoneal recurrence in obese GC patients.