Retropubic radical prostatectomy (RRP) may involve major intraoperative blood loss. This study focuses on how limited intraoperative hydration, especially in the early part of the surgery, affects the total blood loss. Fifteen prostate cancer patients were enrolled in this study in which the RRPs were performed by a single surgeon with limited (no more than 1500 ml as a rule) intraoperative hydration in the first 2 hours of the surgery when ligation of intrapelvic lymph node, dorsal vein complex (DVC), neurovascular bundle (NVB) and cut of urethra are assumed to be finished, and were compared with the control group in which no intervention of hydration was undertaken. Intervention group (n=15) had significantly less intraoperative blood loss (p<0.05) compared with control group even though blood pressure at the first 2 hours was not significantly different. Limited hydration did not cause apparent adverse events resulted from dehydration. In conclusion, limited hydration especially in the first half of operation may reduce intraoperative blood loss without any side effects of dehydration. This study could help to establish detailed guidelines for hydration methods for less blood loss during RRP.