6588 Background: Elderly patients are concerned with the physical burden of cancer treatments. This study aimed at investigating the reduction of the activity of daily living (ADL), length of hospital stay and readmission rate after surgery for gastric cancer. Methods: Insurance claim data linked with hospital-based cancer registries in Japan for gastric cancer patients diagnosed in 2015 from 431 hospitals was used. This data is expected to cover 49.0% of new cancer cases in Japan. To compare the effect of the treatment by age group, we analyzed the reduction of ADL between admission and discharge, length of hospital stay and readmission rate after endoscopic submucosal dissection (ESD) or endoscopic mucosal resection (EMR) for patients with cT1N0M0, and open surgery for patients with cM0. Patients who aged 40 years or older with independent ADL at admission for their first-course treatment was included. ADL was assessed using Barthel index (0-100 points). ADL decrease by 10 points or more was identified as ADL reduction. Results: Overall, 25,521 patients receiving ESD/EMR and 10,527 patients receiving open surgery were identified. ADL reduction after ESD or EMR under 80 years old was less than 1%, while over 80 years old ADL reduction was more than 2.5%. Length of hospital stay (11 days) and unexpected readmission rate (2 to 3 %) was almost similar. ADL reduction after open surgery under 75 years old was less than 3%. This reduction rates have increased with age, 11.5% for over 85 years old. Length of hospital stay also tended to increase by age (21 days for under 65 years old, 29 days for over 85 years old). Unexpected readmission rate for over or 80 years old (1.4%) was slightly higher under 80 years old (less than 1%). Conclusions: The effect of ADL reduction after ESD/EMR was not so significant for patients over 80 years old. While ADL reduction after open surgery tended to increase for aged 80 years and older. Providing these information to elderly patients and their families can be important in deciding treatment options.[Table: see text]