Vitamin B(sub)12(cobalamin) is an essential nutrient in human and it is particularly important during pregnancy. Nevertheless very few studies have reported, concerning vitamin B(sub)12 in relation with reproduction. This study was conducted to evaluate the vitamin B(sub)12 nutrition status of Korean pregnant women and to investigate the relationship between serum vitamin B(sub)12 levels of maternal-umbilical cord blood and pregnancy outcomes. Dietary vitamin B(sub)12 intakes of the pregnants were estimated by semiquantitative frequency questionnaire. Serum vitamin B(sub)12 levels in both maternal blood and umbilical cord blood of 30 pregnant women at delivery were measured by radioimmunoassay. Mean vitamin B(sub)12 intake was 3.3$pm$1.4$mu extrm{g}$/d which was 125.8% of the Korean RDA(2.6$mu extrm{g}$) for vitamin B(sub)12 level of umbilical cord blood was 607.8$pm$282.9pg/ml, more than two fold of maternal vitamin B(sub)12 level 268.6$pm$97.8pg/ml. This finding indicates that fetal uptake of vitamin B(sub)12 in the fetus may be due to an active transport mchanism across the placenta. Umbilical cord blood vitamin B(sub)12 levels were highly correlated with maternal levels($r^2$=0.548, p<0.001), showing that fetal vitamin B(sub)12 level is affected by maternal status. However there was no significant correlation between the serum vitamin B(sub)12 levels in maternal-umbilical cord blood and the pregnancy outcomes except for the birth weight. Maternal-umbilical serum vitamin B(sub)12 levels were the highest in the group of birth weight 3.0-3.5kg, and the lowest in the group of birthweight below 3.0kg. (Korean J Nutrition 34(4) : 426~432, 2001)