Phytosterol derived from plants has long been used for the medical treatment of benign prostatic hyperplasia (BPH) in Europe but not in Japan. The efficacy of phytosterol was evaluated in patients with manifestations of urinary outlet obstruction caused by BPH. Phytosterol containing 180 mg of sitosterol per day was given to 12 patients with BPH in two or three divided doses for three months. The symptoms were assessed monthly using the International Prostate Symptom Score (IPSS) and quality-of-life (QOL) score while the objective findings including the urinary flow, prostatic volume, and residual urine volume were assessed after three months of treatment of BPH. The IPSS and QOL scores showed significant improvement (p < 0.05), and the peak flow rate and residual urine volume showed slight but not significant improvement.