Background: There has been no established regimen as the second-line treatment for advanced gastric cancer (AGC), though CPT-11 showed survival benefit over BSC. Combination of CPT-11 with CDDP is one of the promising regimens as the second-line chemotherapy after S-1 mono-therapy. Methods: This is a prospective, multicenter randomized phase III study comparing CPT-11+CDDP (Arm A) vs. CPT-11 alone (Arm B) in patients with advanced or recurrent gastric cancer resistant to S-1 mono-therapy or prior adjuvant chemotherapy using S-1. Eligibility criteria include histologically confirmed gastric adenocarcinoma, age over 20 years old, PS: 0-2, adequate organ functions and written informed consent. Arm A: patients received CPT 11 60mg/m² and CDDP 30mg/m² on day 1, q2w. Arm B: patients received CPT-11 150mg/m²on day 1, q2w. Stratification was made according to PS, advanced or recurrence cases, institution and presence or absence of measurable target lesions. Primary endpoint was overall survival (OS), secondary endpoints were progression free survival (PFS), time to treatment failure (TTF), response rate (RR), and safety. Results: 168 patients were registered between 2007 and 2011. Arm A (n=84) and Arm B (n=84) were well balanced for baseline factors. Median age was 67 vs 68 years old, number of advanced/recurrence after resection was 36/48 vs 35/49, and median number of treatment course was 5 vs. 6 (range:0-31, 0-39). Common grade 3/4 toxicities in Arm A vs. Arm B were neutropenia; 35.4% vs. 27.2% (p=0.259), anemia; 15.9% vs. 3.7% (p=0.009), diarrhea; 0% vs. 2.5% (p=0.152), nausea; 3.7% vs. 4.9% (p=0.687), vomiting; 1.2% vs. 3.7% (p=0.305), anorexia 6.1% vs. 8.6% (p=0.534). The rate of patients who were required dose modification for these toxicities was 22.9% vs 21.4%. The pooled OS, PFS and RR for both Arms were as follows; 13.8 months (95% CI, 10.7 to 17.5), 4.5 months (95% CI, 3.7 to 5.1), and 13.7%. Conclusions: There was no significantly difference in the incidence and severity of adverse events in both Arms except for anemia. Updated efficacy data of secondary endpoints will be presented. Clinical trial information: UMIN000002571.