Desired family size and ideal family size were examined by using a sample of 300 married women who came to the Institute for Protection Mother and Newborn in Hanoi, Vietnam for gynecology treatment and delivery in November 1991. Desired family size was measured on the basis of the number of children a women wants to have during her life. Ideal family size is a womans opinion on an appropriate family size for a married couple. Factors affecting both desired and ideal family size were analyzed which include age, residence, education, occupation, women of marriage and number of living children. The result indicated that older women desired larger family size than those in younger age. Women who lived in urban areas had smaller family size than women who lived in rural areas. Women with higher education had a smaller family size than those with lower education attainment. In addition, women with longer duration of marriage desired more children than those who had shorter duration of marriage.