Child mortality is the mortality of children under the age of five. The child mortality rate, also under-five mortality rate, refers to the probability of dying between birth and exactly five years of age expressed per 1,000 live births.

It encompasses neonatal mortality and infant mortality (the probability of death in the first year of life).

Reduction of child mortality is reflected in several of the United Nations' Sustainable Development Goals. Target 3.2 is "by 2030, end preventable deaths of newborns and children under 5 years of age, with all countries aiming to reduce … under‑5 mortality to at least as low as 25 per 1,000 live births."

Child mortality rates have decreased in the last 40 years. While in 1990, 12.6 million children under age five died, in 2016 that number fell to 5.6 million children, and then in 2020, the global number fell again to 5 million. Rapid progress has resulted in a significant decline in preventable child deaths since 1990, with the global under-5 mortality rate declining by over half between 1990 and 2016. While in 1990, 12.6 million children under age five died, in 2016 that number fell to 5.6 million children. However, despite advances, there are still 15,000 under-five deaths per day from largely preventable causes. About 80 per cent of these occur in sub-Saharan Africa and South Asia, and just 6 countries account for half of all under-five deaths: China, India, Pakistan, Nigeria, Ethiopia and the Democratic Republic of the Congo. 45% of these children died during the first 28 days of life. Death rates were highest among children under age 1, followed by children ages 15 to 19, 1 to 4, and 5 to 14.