Background/Aims: Monascus Adlay (MA) prepared from fungal fermentation of Monascus purpureus inoculating with cooked adlay contains high content of monakolin K (MK) and phenolic compounds. We explored whether MA and MK improve FeCl3-induced arterial thrombosis in rats. Methods: The rats were divided into control, FeCl3-treated rat carotid artery occlusion (TTO), TTO determined with one-week MA, and TTO determined with one-week MK. We compared MA or MK effects on oxidative stress by chemiluminescence amplification and immunohistochemistry, TTO by a transonic system, NFκB, ICAM-1, endoplasmic reticulum stress CHOP and Nrf2 signaling by western blotting. Results: MA or MK efficiently depressed O2-, H2O2 and HOCl levels, platelet activation and aggregation and H2O2-enhanced ICAM-1 and VCAM-1 expression in the endothelial cells. FeCl3 significantly increased NFκB p65, 3-nitrotyrosine, CHOP and ICAM-1 expression, and decreased nuclear Nrf2 translocation and induces arterial thrombus formation. MA or MK pretreatment significantly elongated the level of FeCl3-induced TTO compared to TTO group, significantly decreased proinflammatory NF-κB/ICAM-1 signaling, endoplasmic reticulum stress CHOP expression and decreased thrombotic area. MA or MK significantly preserved nuclear Nrf2 translocation. MA and MK exerted a similar protective effect in attenuating thrombus formation. Conclusions: We suggest MA is better than MK to improve FeCl3-induced arterial thrombosis.