Building on the conservation of resources model, we conducted three studies to explore the link between ambient temperature and individual prosocial behavior. In study 1, analyzing the two‐wave field data from a chain of retail stores in Eastern Europe, we find that, in hot, as opposed to normal temperatures, employees are less likely to act in a prosocial manner. In study 2, we replicate and extend these findings in a randomized controlled experiment by identifying mechanisms underlying the relationship between hot ambient temperature and helping behavior. Specifically, we find that heat increases fatigue that leads to reduction in positive affect and subsequently reduces individual helping. Finally, in study 3, we replicate these findings in a field experiment. Taken together, our study helps to explain how and through what mechanisms ambient temperature influences individual helping. The theoretical and practical implications of our findings are discussed.