Intravesical botulinum toxin A (BoNT-A) injection is effective and has been approved in the treatment of overactive bladder (OAB) syndrome in patients who are refractory or intolerable to antimuscarinic therapy. Intravesical BoNT-A injection increases bladder capacity, decreases detrusor pressure, and reduces the urgency sensation in OAB patients. Although clinical experiences have demonstrated a dose-dependent therapeutic effect of BoNT-A, the adverse events such as acute urinary retention, voiding difficulty, large post-void residual, and subsequent urinary tract infection remain problematic and increase with higher doses in frail elderly patients. Currently, 100 U of onabotulinumtoxinA has been approved by many countries for the treatment of patients with non-neurogenic OAB. The duration of therapeutic effect is around 6 to 9 months and usually remains the same after repeat treatments. The injection sites can involve the bladder wall with or without sparing the trigone. Gathered experience has also shown that BoNT-A injection is also effective in the treatment of OAB symptoms in children and in patients with stroke or Parkinson’s disease. Before BoNT-A injection, physicians should learn the injection technique and inform the potential adverse events to patients who desire this treatment.