Wu Pei San (烏貝散，W.P.S.) is composed of cuttlefish bone (wu zei gu) and Zhechiang fritillaria (zhe bei mu). It is one of the basic formulas for treatment of epigastralgia in Chinese Medicine. The purpose of this study is to evaluate the efficacy of W.P.S. in the treatment of duodenal ulcer with panendoscopic examination. Sixty consecutive cases of active duodenal ulcer diagnosed by panendoscopic examination, randomized into W.P.S. group, 32 cases and Zantac group, 28 cases. The mean ages were 45.5±5.2 and 43.0±6.4 respectively. The ratio of males and females of both group was 21: 11 and 20: 8 respectively. The healing rate of W.P.S. group is 37.5% after 4 weeks treatment and 71.9% after 8 weeks treatment. In Zantac group, the healing rate is 50.0% after 4 weeks treatment and 78.6% after 8 weeks treatment. There is no significant difference between these two groups statistically (P＞0.05). The epigastralgia relief rate is excellent in both groups. The epigastralgia relieved within one week in 50.0% (16/32) in W.P.S. group and 57.1% (16/28) in Zantac group. There is no prominant side-effect noted during and after the course of treatment in both groups. Concomitantly, we found smoking has a close relationship with the healing of ulcer in this study. After 8 weeks treatment, the healing rate for the 28 smokers in both groups was 60.7% (17/28), while that for the 32 non-smokers was 87.5% (28/32). There was no change in hemoglobin and electrolytes in serum before and after treatment in both groups. Our results indicate that: W.P.S. may be an effective, safe formula for the treatment of duodenal ulcer.