Background: Ultrasensitive prostate-specific antigen (USPSA) is useful for stratifying patients according to their USPSA-based risk. Aim of our study was to determine the usefulness of USPSA as predictor of biochemical recurrence (BCR) after robot-assisted radical prostatectomy (RARP). Methods: This retrospective study included 213 prostate cancer patients who had a postoperative USPSA between 0.01 and 0.2 ng/mL and at least 2 years of follow-up. We developed predictive models for BCR with PSA ≥0.2 and ≥0.5 ng/mL. Results: A total of 103 patients (48.3%) had BCR at a median follow-up of 13.3 months. Higher postoperative USPSA (odds ratio [OR] = 4.73, P < 0.01), bilateral positive surgical margin in both sides (OR = 1.32, P = 0.044), higher average PSA rise (OR = 1.67, P = 0.031), ISUP grade group ≥3 (OR = 1.48, P = 0.003), and shorter interval since RARP (OR = 0.58, P < 0.001) were independent predictors of BCR with PSA ≥0.2 ng/mL. Higher postoperative USPSA (OR = 3.85, P < 0.01), bilateral positive surgical margin (OR = 1.34, P = 0.011), ISUP grade group ≥3 (OR = 1.5, P = 0.002), and shorter interval since RARP (OR = 0.61, P = 0.001) were independent predictors of BCR with PSA ≥0.5 ng/mL. The areas under the curve for the first and second model were 0.865 and 0.834, respectively. Conclusion: Ultrasensitive PSA after RARP is a useful prognostic indicator of BCR which could guide postoperative risk stratification and layout follow-up scheduling.