Introduction Although early detection and successful gastrectomy have improved the survival of patients with gastric cancer, long-term health problems remain troubling. We evaluated the prevalence of osteoporosis and its risk factors in long-term survivors of gastric cancer after gastrectomy. Methods We reviewed the medical records of a tertiary hospital between 2007 and 2014 to identify survivors of gastric cancer who had visited our center at around 5 years after gastrectomy. We evaluated their health status, including bone mineral density (BMD). Dual-energy X-ray absorptiometry was used to measure the BMD of the lumbar spine and femur (total and neck area). The prevalence of osteoporosis, defined by a BMD T score <-2.5, was investigated, and clinical variables associated with the presence of osteoporosis were identified. Results A total of 250 survivors were included. The mean age was 54.6 years old, and the median follow-up was 6.0 years. The prevalence of osteoporosis was 34.0% (27.4% for men and 43.6% for women). Older age [odds ratio (OR) 5.50, 95% CI 2.33-13.00], higher alkaline phosphatase levels before gastrectomy (OR 5.67, 95% CI 1.36-23.64), and marked weight loss (>= 20%) after gastrectomy (OR 3.59, 95% CI 1.32-9.77) were independently associated with the presence of osteoporosis. Conclusions In our cohort, osteoporosis was commonly observed in long-term survivors of gastric cancer, and several risk factors for it were identified. To reduce the risk of osteoporosis after gastrectomy, maintaining adequate body weight may be necessary.