Abstract The propose of this study is to evaluate the effect of Botulinum A intradetrusor injection on patients with overactive bladder refractory to oral anticholinergics and safety of the drug. Patients with overactive bladder (excluding patients with neurological or pathological causes) were enrolled in this study, those patients did not benefit of oral medications with anticholinergic effect, and they were assessed for history of their problem and kept a urinary diary for three days before the start of the procedure. They were also examined, and ultrasound for post voiding residue with urinary flow rate was kept in records. Injection of 200 IU of onabotulinom toxin-A in the detrusor muscle. The drug effect was studied one month after injection on patient’s symptoms, including day and night frequency, urgency and urge incontinence by keeping a three days’ urinary diary postoperatively. The maximum flow rate and the post voiding volume were also measured. Postoperative complications in the form of haematurea, urinary tract infection and retention of urine were recorded. There was a significant decrease in the number of voiding during both day and night from 10.7±1.68 SD, 2.09±0.93 SD to 4.407±1.394 SD, 1.257±0.752 SD respectively which is statistically significant difference (t (135) =6.377, P≤0.001), (t (135) =0.837, p≤0.001), this was associated with a reduction in the number of episodes of incontinence from 1.37±0.975 SD to 0.6815±0.676 SD. The postvoiding volume was increased remarkably. Complications includes urinary tract infection and retention of lower tract local effects only. In conclusion, the use of onabotulinom toxin-A in the treatment of refractory overactive bladder is effective in reducing patients’ symptoms and discomfort as well as being a safe option for treatment.