Background: Chemotherapy occasionally converts an initially unresectable gastric cancer to a resectable cancer. However, the association between clinical factors and long-term prognosis after conversion surgery for unresectable gastric cancer has not been investigated. Methods: We retrospective reviewed 36 gastric cancer patients who underwent conversion surgery at our institute between 2005 and 2015. Clinicopathologic characteristics and patient outcomes were analyzed, with particular focus on the potential to predict long-term survival. Results: The number of incurable factors was one in 31 patients and two in 5, including metastases to non-regional lymph node in 22, peritoneum in 10, liver in 6, and lung in 3. The regimen of chemotherapy was Docetaxel/CDDP/S-1 in 23 patients, Docetaxel/CDDP/S-1+Trastuzmab in 7, S-1/CDDP in 2, Docetaxel/S-1 in 1, CPT/CDDP in 1, and S-1 monotherapy in 1. Complete resection with no residual tumor (R0) was achieved in 25 of 36 patients, microscopic residual tumor status (R1) in 10, and macroscopic residual tumor (R2) in 1. The 3-year overall survival (OS) rate among the 36 patients who underwent conversion surgery was 60.3 % (median survival time, 1200 days). The 3-year OS rate among patients who underwent R0 resection was 70.8 % (median survival time, 1503 days). Patients who underwent R0 resection had significantly longer OS times than those who underwent R1 and R2 resection (p=0.0124). We selected 16 variables in addition to residual tumor for Kaplan–Meier analysis. According to the log rank test, the following four variables were significantly associated with a better OS: clinical response to 1^st line therapy (CR or PR vs. SD or PD)(p=0.0283), pathological response grade (1b-3 vs. 0-1a) (p=0.0304), pathological tumor depth (CR or T1~T3 vs. T4) (p=0.0261), and pathological nodal stage (N0〜2 vs. N3) (p=0.0086). Conclusions: Our data indicates that clinical response to 1^st line therapy in preoperative characteristics, R0 resection, pathological response grade, pathological tumor depth, pathological nodal stage in postoperative characteristics are predictive factors that can be expected to long-term survival.