INTRODUCTION: Warm ischemia time (WIT) is a primary concern for robot-assisted laparoscopic partial nephrectomy (RALPN) patients because longer WIT is significantly associated with postoperative deteriorating kidney function. Tumor complexity, determined by the RENAL nephrometry score (RENAL score), can help predict surgical outcomes, but it is unclear what RENAL score and clinical factors affect WIT. This study explored the clinical factors predicting long WIT in RALPN.MATERIALS AND METHODS: In our institute, 174 RALPNs were performed between November 2013 and February 2021, of which 114 were performed by a single surgeon and included in this study. Clinical staging and the total RENAL score were determined based on preoperative CT scans. The cases were divided into three groups based on experience: period 1: 1–38, period 2: 39–76, and period 3: 77–114. The clinical factors associated with longer WIT were analyzed per period. RESULTS: The overall median tumor diameter was 32 mm, and one patient had a positive surgical margin, but there were no cancer-related deaths. In total, there were 18 complications (15.8 %). Periods 2 and 3 had larger tumor diameters (p<0.01) and worse preoperative kidney function (p=0.029) than period 1. A RENAL L-component score of 3 was associated with longer WIT in period 3 (odds ratio: 3.900; 95 % confidence interval: 1.004–15.276; p = 0.044), but the tumor diameter and the total RENAL score were not.CONCLUSIONS: A large tumor in the central lesion indicated by the RENAL L-component score was associated with increased WIT in RALPN.