We evaluated the efficacy and side effects of two-week administration of low-dose "Hachimi-jio-gan (Ba-Wei Di-Huang-Wan)" for 41 patients with benign prostatic hyperplasia and searched for any predictors of good response to this agent. Although two of the 41 patients could not finish administration due to epigastric discomfort, there were no other side effects. "Hachimi-jio-gan" significantly reduced scores of emptying, weak stream, total score and quality of life score according to the International Prostate Symptom Score, although the degree of reduction was inferior to that induced by tamsulosin administration. "Hachimi-jio-gan" significantly improved max flow rate, and the degree of this improvement was superior to that induced by tamsulosin administration. Approximately 40% of patients were good responders to "Hachimi-jio-gan" therapy. Severe sensation of incomplete emptying was a predictor of good response.