To evaluate the efficacy of a second generation acid pump inhibitor-lansoprazole (L) a controlled clinical trial in 72 patients of duodenal ulcer was carried out with omeprazole (O) as control. The results showed that the ulcer healing rate after 4-week treatment was 97.4% in lansoprazole group and 91.2% in omeprazole, while the effective rate was 100% and 97.1% respectively (P > 0.05). Ulcer related pain was relieved more quickly in lansoprazole group. The pain relief rate after treatment of 3 days was different significantly between the two group, being 74.3% (L) and 51.6% (O) respectively (P < 0.05). No marked side-effect was observed in lansoprazole group. It is shown that lansoprazole is effective and safe for treatment of duodenal ulcer.