Objective: The aim of this study was to report our preliminary experience of the treatment with mirabegron and to identify the predictors of a successful treatment with mirabegron in overactive bladder (OAB) patients. Materials and methods: Between October 2015 and February 2016, 234 consecutive patients (167 men and 67 women; mean age: 65.6 years; standard deviation: 16.3) diagnosed with OAB and receiving mirabegron monotherapy were enrolled retrospectively. Four weeks after mirabegron treatment, a global response assessment (GRA) was performed for all patients and analyses were performed to identify possible predictors of successful mirabegron treatment (defined as GRA ≥ 1). Mirabegron was intended being given for at least 12 weeks. Adverse events (AEs) and reasons for discontinuing mirabegron were recorded between 4 and 12 weeks of following-up. Results: The rate of successful mirabegron treatment (GRA ≥ 1) was 70.5%. The proportion of patients with a successful response was significantly higher in men than in women (75.3% vs. 60.5%, p = 0.022). The success rates as well as the percentage of older patients between groups with or without diabetes, hypertension, nocturia, urge incontinence, or prior anticholinergic treatment were not significantly different. Multivariable analysis showed that male sex was a significant independent predictor (p < 0.05) for successful treatment. The overall rate of AEs was 3.8%, including five cases with hypertension (2.1%) and three with severe voiding difficulty (1.3%). A total of 136 patients (58%) were administered mirabegron for more than 12 weeks. The reasons for discontinuing mirabegron included symptom improvement (17%), loss to follow-up (13%), poor treatment efficacy (8%), and side effects (4%). Conclusions: The success rate of mirabegron treatment for OAB patients was high and the rate of overall AEs was low. Although only 58% patients continued mirabegron at 12 weeks, most patients (17%) discontinued the treatment because of reduction in symptoms. Male sex showed better response to mirabegron treatment.