Purpose: As body weight management is significantly important for women and newborn infants during pregnant and postpartum periods, there have been studies about changes of body weight during those periods. However, there are not enough studies about it which is based on the Sasang Constitution. The following is a result of the study which analyzes the changes with Sasang Constitution. Methods: This study investigated those who understand and agree this study#s purposes out of 109 primiparae who did normal delivery, who gave birth to a healthy infant and who are breastfeeding and who were treated by S postpartum care center from March 2005 to November 2005. The result of survey was collected from the questionnaires that included postpartum pattern and QSCC II. Results: There are remarkable changes of body weight and BMI based on the Sasang Constitution in pregnant and postpartum periods and they appear to be in order of Taeumin, Soyangin, Soeumin. In terms of the amount of milk according to the Constitution, there are no key changes between Soeumin and Taeumin, but there is a significance between Soyangin and Soeumin and Soyangin and Taeumin. In terms of the average body weight of infants according to the Constitution, there are no essential changes between Soeumin and Soyangin, but there is a magnitude between Soeumin and Taeumin and Soyangin and Taeumin. Conclusion: The changes of the body weight and BMI based on the Sasang Constitution appear to be the smallest for Soeumin, and the largest for Taeumin. The amount of milk from mothers did not affect on the changes and the weight of newborn infant did affect on the changes.