Along with the country’s socio-economic development, Vietnamese families have undergone considerable changes. These changes can be clearly se en in the obvious decline in household size. This success is attributed to Vietnam’s population and fami ly planning policy and the change in model of multi- generation living together which has existed for thousa nds of years now. Nonetheless, the reduction in household size is also due to such negative factors as the increasing divorce rate of couples or the trend that a part of the population, especially young people do not want to get married or give birth in order to enjoy their own life. Across the country, single household account for a very low proportion. Small household size (households with 4 members or fewer) is common in our country, especially in urban areas. Generally, rural household size is larger than urban one throughout the country. In terms of geographic regions, the Central Highlands has the largest household size; the second is the Northern Midlands and Mountainous areas. The Red River Delta is the region with the smallest household size. Household size is inversely proportional to incomes of household. Household with the highest incomes (quintile 1) has the smallest size; in contrast, the poorest household (quintile 5) has the largest one. If the correlation between household size and genders of household heads is considered, female-headed households are smaller than male-headed households.