AbstractThe Great Chinese Famine (1959–1961) claimed tens of millions of lives. This study aims to causally examine the long‐term mental health cost it imposed on those who survived. To estimate the nationwide total mental health cost, we use a novel dataset to measure the famine intensity of every prefecture‐level region, match it to a nationally representative survey, and then identify the long‐term effects of the famine on the depression of rural residents then in the early years of their lives. Difference‐in‐differences estimates reveal that a one‐standard‐deviation rise in the experienced famine intensity increased a standard measure of depression by about 0.039 and 0.064 if the individual experienced the famine at ages 0–2 and 3–5, respectively. This translates into roughly 7.99 million cases of severe depressive symptoms caused by the famine, which is likely an undercount. Examining the mechanisms behind the large effects, we find that important roles were played by starvation experience and childhood maltreatment, as well as the primary mediators including other health outcomes, economic status, and social relationship. Our findings shed light on how large‐scale food security failures impact the mental well‐being of the survivors.