In addition to inhibiting cyclooxygenase and prostaglandin, nonsteroidal anti-inflammatory drugs (NSAIDs) may cause gastroduodenal injuries due to reactive oxygen species produced by recruited inflammatory cells. DA-9601 is a novel antioxidant with anti-inflammatory and cyto-protective effects. This study was conducted to compare the efficacy and safety of DA-9601 with misoprostol for preventing NSAID-associated gastroduodenal injury. In this randomized, double-blind, multicenter, noninferiority trial we compared the extents of protection of gastric and duodenal mucosae by endoscopy after 4 weeks of treatment with DA-9601 60 mg or misoprostol 200 µg three times daily, in subjects with normal baseline endoscopic findings who received an NSAID twice daily for 4 weeks. A total of 266 subjects were randomized to treatment. At week 4, the gastric protection rates with DA-9601 and misoprostol were 85.1% and 95.2%, respectively; the difference between the groups was -10.1% (var = 0.001), which was shown to indicate noninferiority of DA-9601 compared to misoprostol. Adverse events were lower in the DA-9601 group, 56.4% (95% CI, 48.0%-64.8%) than in the misoprostol group, 69.2% (95% CI, 61.3%-77.0%) (P = 0.031). DA-9601 is not inferior to misoprostol for preventing NSAID-associated gastroduodenal injury, and superior to it with respect to treatment-related side effects.