Introduction: Acute urinary retention is one of the most significant complications of benign prostatic hyperplasia. Until now, standard treatments include catheterization and use of -blockers. Tadalafil has been recently seen to also play a role in the treatment of urinary symptoms caused by benign prostatic hyperplasia. The aim of this study was to survey the addition of tadalafil to tamsulosin in the treatment of acute urinary retention in patients with benign prostatic hyperplasia. Materials and Methods: This is a randomized, double-blind placebo-controlled clinical trial. In all, 80 patients with benign prostatic hyperplasia-related acute urinary retention referred to the emergency department of the hospital were divided into two groups of 40 each and randomly assigned to receive either 0.4mg tamsulosin plus placebo or 0.4mg tamsulosin plus 10mg tadalafil daily for 7days. At the same first visit, the catheter was removed and the ability to void in 24h and 1week later was assessed in each group. Results: The differences in age, urine retention volume, history of drug use, lower urinary tract symptoms, and previous acute urinary retention were not significant between the two groups (p=0.619, 0.149, 0.501, 0.284, and 0.371, respectively). After catheter removal, 23 (57.5%) patients in the placebo group and 26 (65%) in the tadalafil group voided successfully at 24h (p=0.491). After 1week, 29 (72.5%) patients taking placebo and 26 (65%) taking tadalafil could void, yet indicating no significant difference (p=0.469). Conclusion: Addition of tadalafil to -blockers has no significant advantage in improving benign prostatic hyperplasia-related acute urinary retention versus tamsulosin alone.