In order to further investigate the radical scavenging and anti-arteriosclerotic activities of vitamin K2 and estradiol, the comparative effects of vitamin K2 and estradiol on aortic calcium (Ca) and inorganic phosphorus (P) levels in the aorta and the elastin fraction (fr.) were investigated in male rats after experimental arteriosclerosis with diabetes mellitus was induced by vitamin D2 and radical producing substance, streptozotocin (STZ). Pharmacological dose of vitamin K2 (100 mg/kg b.w.) and medical dose of estradiol (83 micrograms/kg b.w.) suppressed the increased serum glucose, and vitamin K2 and estradiol increased the decrease in serum insulin. Moreover, vitamin K2 and estradiol inhibited the increase of Ca and P in the aorta and the elastin fr. Vitamin K2 and estradiol decreased the increase in serum lipid peroxide (LPO). It is suggested that both the pharmacological dose of vitamin K2 and medical dose of estradiol suppressed the development of arteriosclerosis associated with diabetes mellitus, owing to radical scavenging activity of vitamin K2 and estradiol.