Recently, the investigations were focused on Vitamin D and calcium nutrition during pregnancy. There exist the controversies on the Vitamin D status during pregnancy. Our study observed the changes of Vitamin D regulation system during pregnancy. 31 pregnant women studied in the obstetrics units in two hospitals of Chongqing from the Winter of 1992 to the Spring of 1993. After first blood samples from the mothers were taken in 32 weeks of gestation, the oasses were divided into two groups: supplement group (by received 200000 IU of Vitamin D3) and control group. Without supplement Second blood samples were collected from the maternal and umbilical veins during the deliver. All the samples were measured the concentrations of serum 25-OHD3, PTH, CT, calcium, phosphorus and ALP results showed that the serum 25-OHD3 levels of umbilical vein in control group were lower than that in the supplement group. But there were no any manifestations of rickets in the newborns. Except the serum PTH levels of the newborns in supplement group, the concentrations of serum calcium, phosphorus, and CT were same with the newborns in the control group. The trend of serum 25-OHD3 levels of the mothers in the control group was toward decreased during the pregnancy. The levels of ALP in the maternal blood were increased and the concentrations of serum calcium, phosphorus, PTH and CT were relative stability. Although the concentrations of serum 25-OHD3 in the mothers received 200000 IU Viamin D3 in 32 weeks of gestation were increased, which were 2 times of contol group, there were no significant changes of the serum PTH, CT, calcium and phosphorus levels to be observed. The concentrations of ALP in the maternal blood were remarkably higher than that in the umbilical blood in both groups. There was the positive relation of serum 25-OHD3 levels between the maternal and umbilical blood. But there was no relation of the serum calcium levels between the maternal and umbilical blood. Our study demonstrated that the increased values of serum 25-OHD3 in the mothers received supplement Vitamin D3 during the pregnancy can not be used as the indicator to diagnose the Vitamin D deficiency of mother or their baby. The pregnancy is a special physical process, Usually, a health woman will be graduaL ly adapted the physical changes to meet the requirements of own body and her fetus. Howev- er, it may be benefit to prevent the rickets of the baby in 1-2 months of life if the mother takes the suitable dose of Vitamin D3 during the third trimester of gestation. Recently, the investigations were focused on Vitamin D and calcium nutrition during pregnancy. There exist the controversies on the Vitamin D status during pregnancy. Our study observed the changes of Vitamin D regulation system during pregnancy. hospitals of Chongqing from the Winter of 1992 to the Spring of 1993. After first blood samples from the mothers were taken in 32 weeks of gestation, the oasses were divided into two groups: supplement group (by received 200000 IU of Vitamin D3) and control group. Without supplement Second blood samples were collected from the maternal and umbilical veins during the deliver. All the samples were measured the concentrations of serum 25-OHD3, PTH, CT, calcium, phosphorus and ALP results showed that the serum 25-OHD3 levels of umbilical vein in control group were lower than that in the supplement group. But there were no any manifestations of rickets in the newborns. Except the serum PTH levels of the newborns in supplement group, the concentrations of serum calcium, phosphorus, and CT were same with the newborns in the control group. The trend of serum 25-OHD3 levels of the mothers in the control group was toward decreased during the pregnancy. The levels of ALP in the maternal blood were increased and the concentrations of serum calcium, phosphorus, PTH and CT were relative stability. Although the concentrations of serum 25-OHD3 in the mothers received 200000 IU Viamin D3 in 32 weeks of gestation were increased, which were 2 times of contol group, there were no significant changes of the serum PTH, CT, calcium and phosphorus levels to be observed. The concentrations of ALP in the maternal blood were remarkably higher than that in the umbilical blood in both groups. was the positive relation of serum 25-OHD3 levels between the maternal and umbilical blood. But there was no relation of the serum calcium levels between the maternal and umbilical blood. Our study demonstrated that the increased values ​​of serum 25-OHD3 in the mothers received supplement Vitamin D3 during the pregnancy can not be used as the indicator to diagnose the Vitamin D deficiency of mother or their baby. The pregnancy is a special physical process, Usually, a health woman will be graduaL ly adapted the physical changes to meet the requirements of own body and her fetus. Howev er, it may be benefit to prevent the rickets of the baby in 1-2 months of life if the mother takes the appropriate dose of Vitamin D3 during the third trimester of gestation.