Abstract: Objective To understand the situation and main causes of children death under five years old in Lanzhou City from 2010 to 2014 and provide scientific basis for improving child health care to further reduce under-five mortality rate. Methods The death reporting categorized cards of children under five years old from 2010 to 2014 were used to analyze the distribution of age and causes of death, the potential years of life lost (PYLL) was assessed. Results The average mortality of children under five years old was 7.97‰ and neonatal death accounted for 69.61%. The top six leading causes of death were preterm delivery or low birth weight, birth asphyxia, congenital heart disease, other congenital anomaly, pneumonia and accidental death. The index of potential death caused by the top six leading causes were 71.73, 71.73, 71.42, 71.60, 71.64 and 69.47 respectively. The per PYLL of children under 5 years old was 71.44 (84157.94/1178). Conclusions We should actively control the main causes of children death under five years old, improve the construction of obstetrical and pediatrics department, and popularize the use of PYLL and the index of potential death in child care evaluation as early as possible.