Gastrointestinal toxicity due to non-steroid anti-inflamatory drugs can be inhibited by the compounds that have antioxidant activity. Quercetin is a flavonoid that has antioxidant activity and protection effect against ulcer. Chlorination of quercetin anhanced the antioxidant. This study aims to obatin the chlorinated derivative of quercetin and examine the protection effect against acetosal-i…