The incidence of gastric cancer in older people is increasing. Because older patients are at increased risk of postoperative complications and mortality, preoperative risk assessment in this population is important. This study explored whether preoperative assessment of frailty could be useful for predicting the postoperative outcome in patients with gastric cancer. We investigated 223 patients (136 men and 87 women) over 65years of age who underwent gastric cancer surgery from April 2012 to March 2015 at a single institution in Korea. Frailty was assessed using the Study of Osteoporotic Fractures (SOF) frailty index. Logistic regression was used to identify factors predicting readmission within one year of discharge following gastrectomy. Twenty six (11.7%) patients were readmitted within one year after gastrectomy. Patients in the "robust" and "pre-frail and frail" group had a readmission rate of 6.7% and 19.1%, respectively. After adjusting age, gender, Eastern Cooperative Oncology Group performance status (ECOG PS) (score≥1), histological type and stage (III, IV), frailty (pre-frail and frail) was a predictive factor for readmission within one year of discharge after gastrectomy (Odds Ratio, 5.74, 95%; Confidence Interval, 1.78-18.48; p=0.003). Preoperative risk assessment including frailty evaluation can predict the readmission within one year of discharge after gastrectomy. Frailty assessment can help physicians to identify the risk and inform patients and their families of the risk, which should improve decision making in gastric cancer treatment.