Intravesical prostatic protrusion (IPP) is associated with the degree of benign prostatic obstruction. We evaluated the effects of Mirabegron, a selective β3 adrenoceptor agonist, on overactive bladder (OAB) in male patients with different degrees of IPP. About 185 male patients ≥40years with lower urinary tract symptoms were recruited from a tertiary referral center. OAB was defined by the overactive bladder symptom score (OABSS) urgency score of ≥2 and sum score of ≥3. IPP was measured in the midsagittal section using transrectal ultrasound and patients were divided into IPP ≤5mm and IPP >5mm groups. Outcomes were assessed at the baseline, 4, and 12weeks. About 104 patients (56.2%) were diagnosed with OAB and received Mirabegron (50mg) daily use. Both IPP groups (≤5 and >5mm) had similar baseline OABSS and International Prostate Symptom Scores (IPSS). Four-week Mirabegron usage was associated with significant decreases in both symptom score measurements, OABSS: IPP ≤5mm -27.4% and IPP >5mm -19.7% (P=.419) and IPSS: -32% and -22.5% (P=.202), respectively. Urgency, urge incontinence, and nocturia sub-scores were decreased in both groups, -26.3% and -27.4% (P=.690), 53.3% and 46.2% (P=.916), and 20.8% and 15.4% (P=.958). Effects were maintained at 12weeks. We found no significant improvement in the frequency sub-score in either group. One patient stopped medication because of intolerable hypertension. Most frequent adverse event was increased residual urine (≥50mL higher than baseline), IPP ≤5mm 9.2% and IPP >5mm 5.1% (P=.707), but no case had acute urinary retention. Mirabegron is an effective drug to treat male OAB regardless of IPP grade.