OBJECTIVE: To study the underfive mortality rate and the causes of death in Zhejiang Province between 2000 and 2009 in order to provide a basis for reducing the mortality rate in the region. METHODS: By stratified random cluster sampling, all the children under 5 years old from 30 sampling areas of Zhejiang Province between 2000 and 2009 were enrolled. The under-five mortality rate and the leading causes of death were investigated by descriptive analysis and Chi-square test. RESULTS: The under-five mortality rate demonstrated a decreased trend in Zhejiang Province between 2000 and 2009, with the under-five mortality rate of 14.83‰ in 2000 compared to 9.49‰ in 2009. In 2009, the under-five mortality rate in rural regions was significantly higher than that in urban regions (9.14‰ vs 6.50‰; P<0.01). Compared with the resident population, there were an increased under-five mortality rate in floating population (12.12‰ vs 6.42‰; P<0.01). Preterm delivery/low birth weight was the top death cause in children under 5 years old. The top three causes of death in infants less than 1 year old were preterm delivery/low birth weight, congenital heart disease and birth asphyxia compared to drowning, traffic accident and falling in children aged 1-4 years. CONCLUSIONS: There are differences in the under-five mortality rate between rural and urban children as well as between the floating and resident population in 2009. The leading causes of death in different age groups are different. It is essential to reduce the mortality rate by preventing preterm delivery, low birth weight and congenital malformations to infants and preventing accidental injuries to children aged 1-4 years.