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Quercetin (3,3’4’,5,7-pentahydroxyflavone) has been reported to show anti-inflammatory activity. However, its low oral bioavailability limits the application of quercetin in therapy. Ester derivatives of quercetin have been reported to have higher bioavailability than quercetin. This research aimed to study the anti-inflammatory activities and gastric ulcer-inducing properties of tetraacetylquercetinas well as tetrapivaloylquercetin. Synthesis of tetra-acyl derivatives of quercetin was conducted using acetic anhydride or pivaloyl chloride in the presence of pyridine and the structure was confirmed by 1H-NMR and 13C-NMR spectroscopy as well as elemental analysis. At a dose of 20 mg/kg bw, oral administration of quercetin only showed 20% inhibition activity on carragenan induced rat paw edema, while tetraacetyl and tetrapivaloyl derivatives at equimolar dose showed 11-33% and 5-15% inhibition activity respectively. Contrary to the gastric ulcer healing-promoting action of quercetin, tetraacetylquercetin caused mild gastric ulcers. However, no gastric ulcer was observed after administration of tetrapivaloylquercetin. It was concluded that acylation enhances the anti-inflammatory activity of quercetin but causes mild gastric ulcers in the case of tetraacetylation.