Background: Although Isorhamnetin (ISO); a natural flavonoid compound, was shown to have strong antioxidant and antifibrotic effects in vivo and in vitro. The aim of his study was to evaluate the ISO effect on angiotensin-II (Ag-II) induced atrial fibrillation (AF) in mice. Methods: Wild-type male mice (C57BL/6J, 8 weeks old) were assigned into 3 groups; control (Cont) group, Ag-II group treated with only Ag-II, and Ag-II & ISO group treated with Ag-II and ISO. Ag-II (1000 ng/kg/min) was continuously administered by an implantable osmotic pump for 2 weeks, and ISO (5 mg/kg) was administered intraperitoneally one week before starting Ag-II administration. AF induction and electrophysiologic study was performed by transvenous electrode catheter and Ca2+ imaging was also conducted with isolated cardiomyocyte. Gene expression levels of AF-related molecules, and histological examination of atrial fibrosis were also accessed. Results: AF inducibility was dramatically increased by Ag-II and significantly decreased by ISO. AF duration was also remarkably prolonged by Ag-II and significantly reduced by ISO. Atrial effective refractory period (BCL=150msec) was reduced by Ag-II and recovered by ISO. Diastolic intracellular Ca2+ abnormal activities (sarcoplasmic reticulum [SR] Ca2+ leakage) was observed in Ag-II group; however, ISO treatment eliminated these abnormalities. Ag-II induced elevated expression of Ca2+-handling related molecules (Camk2 and Ryr2) and fibrosis-related molecules (Col1a1, Tgfb1 and Tgfb2) were significantly normalized by ISO. Histological examination demonstrated that cell size and the fibrosis ratio were increased by Ag-II, and significantly attenuated by ISO. Conclusion: It was suggested that ISO prevented against Ag-II induced AF vulnerability through both electrophysiological and structural reverse remodeling.