Quercetin-3-glucoside (isoquercitrin) is a flavonol glycoside consisting of quercetin aglycone bound to a glucose moiety at the 3-position. It occurs naturally in onions, apples, tea, and various berries. As a potent antioxidant, it scavenges free radicals, inhibits lipid peroxidation, and exhibits anti-inflammatory and cardioprotective effects via modulation of NF-κB and Nrf2 pathways. It demonstrates improved bioavailability compared to quercetin due to the glycosidic linkage. Used in dietary supplements and functional foods for its health-promoting properties. Chemically stable under acidic conditions but susceptible to enzymatic hydrolysis by β-glucosidases in the gut.