This article includes historical sketch of magnesium research, basic researches on effect of magnesium on cardiovascular disease, practical researches (including clinical studies) on relationship between magnesium intake and cardiovascular disease and current status of intake amount of magnesium in Japanese estimated by the national nutrition survey in Japan, 2002. Basic studies revealed the mechanism that magnesium deficiency may decrease ATPase, leading to increase in intracellular calcium of blood vessels, and then the vasoconstriction occurs in cardiovascular system. Clinical studies clarified that magnesium levels in serum decreased significantly in patients with ischemic heart disease. The National Nutrition Survey in Japan revealed that intake amount of magnesium of people for 15 - 49 year male and female were below the recommended dietary allowance of magnesium in Japan.