To investigate storage symptoms following robot-assisted laparoscopic radical prostatectomy (RARP), focused on de novo overactive bladder (OAB), and to evaluate the factors related to de novo OAB occurrence. We prospectively examined 245 patients without OAB who underwent RARP for localized prostate cancer. Subjective and objective symptoms in the lower urinary tract were evaluated before and after surgery. At 3 months after RARP, the patients were divided into two groups: patients with de novo OAB (de novo OAB group) and those without OAB (OAB-free group). We compared the operative and urodynamic parameters between both groups and evaluated the factors related to OAB. De novo OAB was observed in 37.8% (87/230) of patients. Post-operative continence rate was significantly higher in the OAB-free group (79.7%) than in the de novo OAB group (8.0%). Although the International Prostate Symptom Score (IPSS) and Overactive Bladder Symptom Score (OABSS) in the de novo OAB group significantly deteriorated from 9.7 to 14.1 and from 2.4 to 8.3, respectively, no corresponding significant changes occurred in the OAB-free group. Additionally, there was a significant difference in pre-operative IPSS-QOL score, continence rate, pre-and post-operative maximum urethral closing pressure (MUCP), and post-operative functional profile length (FPL) between both groups. Multivariable logistic regression analysis showed pre-operative IPSS-QOL score and post-operative MUCP were significant predictive factors for de novo OAB. The incidence rate of de novo OAB after RARP was about 40%, and seemed unexpectedly high. Decreased urethral function was significantly related to de novo OAB after surgery.