Background: In spite of the recent advancement of palliative chemotherapy for stage IV gastric cancer (GC), its median survival time (MST) still remains around 13 to 16 months. Much attention has been paid to conversion therapy, however, its definition, operative indication nor survival benefit has not been demonstrated so far. CONVO-GC-1, a retrospective international cohort study, was designed to investigate the role of conversion surgery in Japan, Korea and China. Methods: Conversion therapy of GC was defined as a surgical treatment aiming at an R0 resection after chemotherapy, for tumors that were originally technically and/or oncologically unresectable or marginally resectable. Primary endpoint was the rate of operative complications (Clavien Dindo Grading) and the secondary endpoint was overall survival (OS) according to the 4 category criteria which we have previously published (Gastric Cancer:19; 2016.) (Category 1: resectable metastasis. Category 2: marginally resectable metastasis. Category 3: Macroscopically peritoneal dissemination. Category 4: non-curable metastasis with peritoneal and other organ metastasis.) Results: 1902 patients from 55 institutions were enrolled and 1206 patients (category 1: 206, category 2:583, category 3:300, category 4: 117) were performed surgery after chemotherapy with curative intent. Operative complications were observed in 290 (24.0%) in all grade including pancreatic fistula and SSI etc, which were consistent with other studies (category 1: 19.9%, category 2:29.0%, category 3:18.3%, category 4: 21.4%). The MST of all resected patients were 36.7M (category 1: 42.4 M, category 2: 38.7 M, category 3: 33.4 M, category 4: 34.1 M). The MST of R0 resected patients was 56.6 M (category 1: 49.1 M, category 2: 82.2 M, category 3: 44.9 M, category 4: not reached) and R1 was 25.8 M (category 1: 26.8 M, category 2: 20.3 M, category 3: 30.4 M, category 4: 23.4 M) and R2 was 21.7 M (category 1: 25.0 M, category 2: 22.1 M, category 3: 18.5 M, category 4: 23.5 M), respectively. Conclusions: Conversion therapy for stage IV GC is a safe and might be a new therapeutic strategy to improve the survival of the patients, especially with R0 resection. Clinical trial information: UMIN000022321.