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Overactive bladder (OAB) is defined as urgency, with or without urge incontinence, usually with frequency and nocturia. Antimuscarinic drugs are often prescribed as a standard care; however, the treatment discontinuation due to the adverse events including dry mouth and constipation has been an issue. Taking these situations into account, we considered that a novel OAB drug having a different mechanism from antimuscarinics fills the unmet medical need. It has been known that, during bladder filling, activation of sympathetic nerves results in bladder smooth muscle relaxation via the β-adrenergic receptor (AR) stimulation. In 1999, three Japanese groups independently provided evidence for the existence of β 3 -AR in human bladder smooth muscles and some of these groups showed that β 3 -AR activation is mainly involved in the relaxation induced by β adrenergic stimulation. Therefore, we conducted pharmacological research focusing on β 3 -AR as a novel target molecule for the treatment of OAB. A selective β 3 -AR agonist mirabegron showed the relaxant effect in rat bladder smooth muscle and decreased resting intravesical pressure in anesthetized rats. Mirabegron also improved storage function in a rat detrusor overactivity model. Furthermore, in vitro isometric contraction study using human bladder tissues was conducted to predict the clinical efficacy and mirabegron showed the relaxant effect in human bladder smooth muscle. In clinical studies with OAB patients, mirabegron demonstrated promising efficacy and tolerability. These pharmacological evidences contributed to the approval of mirabegron as a first-in-class drug for OAB treatment in Japan ahead of other countries.