Mirabegron, which was the first b3-adrenoceptor agonist introduced for use in clinical practice, has been extensively evaluated in overactive bladder (OAB) patients in several phase II and III studies. However, most of the enrolled patients were treatment naive or had experienced a wash-out period before the introduction of mirabegron. No study has reported the treatment results of a direct switch from antimuscarinics to mirabegron, which may more commonly occur in clinical practice. This is an observational study to assess the therapeutic efficacy and safety of directly switching from antimuscarinics to mirabegron in patients with OAB receiving stable antimuscarinic treatment. Moreover, we sought to identify the patients who benefited more from the change. Patients aged >= 20 years with OAB receiving stable antimuscarinics for >3 months were enrolled. Antimuscarinics were discontinued in all patients and mirabegron 25mg, once daily was initiated. Primary end-point was global response assessment (GRA) at 1 month after medication switching. Baseline parameters and parameters changed 1 month after medication switching were compared between patients with GRA >= 1 and GRA= 1), 31.2% had similar (GRA=0), and 10.3% had worse (GRA= 1 had significantly improved both storage and voiding symptoms. A total of 195 patients (69.1%) can maintain mirabegron without adding or resuming antimuscarinics for more than 3 months. Logistic regression analysis indicated that higher baseline OAB symptoms scores were predictor of satisfactory outcome. More than 50% patients exhibited better outcomes after switching from antimuscarinics to mirabegron. Significantly lower AE rates and decreased PVR were noted. Higher baseline OAB symptom scores may predict a better outcome.