This trial report describes the background and design for the Japan Intergroup Trial of Pemetrexed Adjuvant Chemotherapy for Completely Resected Nonsquamous Non–Small-Cell Lung Cancer (JIPANG) study (University Hospital Medical Information Network database: UMIN000006737). Various randomized trials have shown the efficacy of postoperative adjuvant chemotherapy regimens that include cisplatin for resected non–small-cell lung cancer (NSCLC), but the optimal regimen is not known. The JIPANG study is a randomized study comparing cisplatin (75 mg/m2, day 1) and pemetrexed (500 mg/m2, day 1) with cisplatin (80 mg/m2, day 1) and vinorelbine (25 mg/m2, days 1 and 8) for nonsquamous NSCLC as postoperative adjuvant chemotherapy. A total of 804 patients with pathological stage II to IIIA completely resected nonsquamous NSCLC were enrolled in this study between March 2012 and August 2016. These patients have been randomized in a 1:1 ratio and stratified according to sex (female vs. male), age (< 70 years vs. ≥ 70 years), pathologic stage (II vs. IIIA), mutation of the epidermal growth factor receptor (mutant vs. wild) and institution. Each treatment will be undertaken every 3 weeks until 4 cycles have been completed. The primary endpoint is overall survival and the secondary endpoints are disease-free survival, rate of treatment completion, and incidence of adverse events. This design has 80% power to detect overall survival with a hazard ratio of 0.786 (α = 1-sided 0.05) with 5-year follow-up after registration of the final patient. This study will show a superior regimen for completely resected nonsquamous NSCLC. Biomarker analyses of the JIPANG study are ongoing.