This study was performed to investigate the effect of Seidlitzia rosmarinus on the clinical symptoms of benign prostatic hyperplasia.This single-blind clinical trial included 98 patients with voiding and storage symptoms in Shohada Ashayer Hospital of Khorramabad. The patients were randomly divided into two groups of treatment with prazosin 1mg/day plus Seidlitzia rosmarinus 3g/day and treatment with prazosin 1mg/day. The clinical symptoms were measured using the International Prostate Symptoms Score (IPSS) questionnaire. Serum prostate-specific antigen (PSA) level, prostate volume, and residual urine volume before and 2 months after the intervention were measured.The results of the study before the intervention did not show significant differences between the prazosin and Seidlitzia rosmarinus plus prazosin groups for the scores of clinical symptoms, PSA level, prostate volume, and residual urine volume (p>0.05). However, significant differences were found between the two groups after the intervention for the mean change scores of clinical symptoms (6.8 scores in the Seidlitzia rosmarinus group vs. 2 scores in the control group) (p0.05).The results of the study showed that the simultaneous consumption of Seidlitzia rosmarinus and prazosin, compared to the consumption of prazosin alone, results in significant improvements in the clinical symptoms of benign prostatic hyperplasia.