Objective To study the relationship between magnesium level in umbilical vein and mother′s peripheral blood with intrauterine growth retardation (IUGR) and fetal weight. Methods 39 pregnant women with IUGR were randomly divided into 3 groups: Group 1 (n= 14): The patients were treated with 10% glucose 500 ml + danshen compound 14 ml + low molecular weight dextran 500 ml iv; Group 2 (n= 14): in addition to the same treatment as in group 1, 25% magnesium sulfate 20 ml in 5% glucose 500 ml iv was given; Group 3 (n= 11): no treatment was given; and another 12 normal term delivery women were served as control. Magnesium concentration levels were determined in both maternal peripheral blood and their fetal umbilical vein. Results Maternal serum magnesium level was higher in Group 2 (1 06?0 09) mmol/L than that in Group 1 (0 69?0 05) mmol/L (P