The purpose of this study is to identify factors affecting family sizes of women in Xiengnguen district of Luangprabang province, Lao PDR. This study uses secondary data on "Contraceptive use among rural married women in Xiengnguen district of Luangprabang province". Findings show most married women have 4 children. A majority of respondents are uneducated and low educated, and have low monthly incomes. About half of the married women are engaged in unskilled labor. The women who are practicing contraception have the larger family sizes. The older aged women (35 and above) have more children than younger women. Almost all women who plan to have larger family sizes have larger numbers of living children. Women with high education are related to smaller family sized. It is also found in the study that women who have education have larger family sizes. Women who work as unskilled labor tend to have larger family sizes. Women who work as farmers have lower family sizes, but women who work in service sectors (government officers and teachers) and housewives have smaller family sizes. Women who are getting married late have smaller numbers of living children. Women who have low income are found to have larger numbers of living children. women who use contraception are found to have larger numbers of living children. In this study, all the demographic variables are positively associated to the number of living children. Among socio-economic factors, only monthly income is found statistically different but it is negatively associated to the number of living children. In this case, the relationship between factors is very low in the expected direction.