BACKGROUND Sexual dysfunction is common after radical prostatectomy (RP). Although pelvic-floor muscle exercise (PFME) has been recommended for sexual dysfunction, the optimal time for starting exercises after this surgery and the effects of exercise still need to be examined. OBJECTIVES The present study was intended to explore the prevalence of sexual dysfunction and to assess the efficacy of PFME in sexual dysfunction following RP. METHODS Participants were randomly distributed into an experimental group (n = 35) or a control group (n = 27). The experimental group took part in PFME as part of regular daily activities after catheter removal post-RP. The control group was taught the exercise in the third month after RP. We followed up the participants at 1, 3, 6, 9, and 12 months. RESULTS All of the patients experienced a severe degree of sexual dysfunction after receiving RP. A t test showed a significant difference in the sexual function mean score between the experimental and control groups at 6 and 12 months. A mixed-model analysis indicated that, after a controlled surgical approach, there was a significant difference in group effect. The experimental group's sexual function was better than the control group's sexual function. CONCLUSION This study demonstrates that early PFME is an effective intervention for sexual dysfunction in prostatectomy patients. The results can help healthcare providers to include this intervention in patients' discharge plans. IMPLICATIONS FOR PRACTICE Patient sexual dysfunction after an RP is common. Nurses should evaluate and manage patients' sexual dysfunction and promote the early return of patients' potency.