Objective of the thesis is to study the effect of α- blocker (TAMSULOSIN HCl) on erectile dysfunction in married men patients who suspected to have benign prostatic hyperplasia. Our study was a prospective randomized study in one to one fashion conducted upon 60 patients, all of them are married, between May 2010 and May 2011, the patients under the study were attending out patient clinic of the New Kasr Al-Aini Teaching Hospital and Students Hospital, Cairo University complaining of lower urinary tract symptoms either obstructive, irritative or both and erectile dysfunction. History was taken from all patients; all patients were examined by digital rectal examination and abdominal examination. We performed pelvic ultrasound, serum P.S.A estimation (patients with P.S.A more than 4ng/ml will do TRUS and biopsy), other routine investigations and uroflowmetry to all patients. Assessment of sexual function changes was by the IIEE (International Index of Erectile Function) and penile Doppler ultrasound. A significant statistical improvement was detected in the erectile function score and intercourse satisfaction score with significant improvement in total IIEF beside the improvement in the IPSS (International Prostatic Symptom Score). While orgasmic function score showed significant worsened, the sexual desire and overall satisfaction score showed no difference between both groups.