Altruism is thought to be a major contributor to the development of large-scale human societies. However, much of the evidence supporting this belief comes from individuals living in pacific and often affluent environments. It is entirely unknown whether humans act altruistically when facing adversity. Adversity is arguably a common human experience (as manifested in, e.g., personal tragedies, political upheavals, and natural disasters). In the research reported here, we found that experiencing a natural disaster affected children’s altruistic giving. Immediately after witnessing devastations caused by a major earthquake, 9-year-olds became more altruistic. In addition, the more empathic they were, the more they gave. In contrast, experiencing a major earthquake caused 6-year-olds to be more selfish. Three years after the earthquake, children’s altruistic tendencies returned to pre-earthquake levels, which suggests that changes in children’s altruistic giving are an acute response to the immediate aftermath of a major natural disaster. These findings suggest that environmental insults and empathy play crucial roles in human altruism.