Abstract: AIM To study the effect of high intake of vitamin K2 on the calcification in rat aorta in vivo. METHODS Rats were divided into normal group (n=6, normal diet) and 6-week calcification group (n=6, 3.0 and 1.5 mg W&K1/g for 6 weeks) and 6 weeks calcification+6 weeks normal group (n=6, 3.0 & 1.5 mg W&K1/g for 6 weeks and normal diet for another 6 weeks) and 12-week calcification group (n=6, 3.0 & 1.5 mg W&K1/g for 12 weeks) and 6 weeks calcification+6 weeks vitamin K2 group (n=6, 3.0 & 1.5 mg W&K1/g for 6 weeks and K2 100 μg/g for another 6 weeks). Alizarin red S and Von Kossa staining was applied to count the calcium nodes and the aorta calcium depositions were measured. RESULTS Continuation of warfarin-containing diet for 12 weeks led to an almost linear increase of the arterial calcium content. High-vitamin K2 intake not only blocked the progress of further calcium accumulation but also led to >39% reduction of previously accumulated arterial calcium precipitates within 6 weeks (60% as compared with what at the 12-week calcification time point, P<0.01). After a 6-week period (weeks 7-12), 40% of the preformed calcium salts had been removed. Compared with those in the calcification group, count of calcium nodes, aorta calcium depositions, alkaline phosphatase activity were reduced in vitamin K2 group (P<0.01). CONCLUSION High intake of vitamin K2 inhibits and/or reverses the calcification in rat aorta in vivo.