Learning from others is one of the main expressions of humans’ social nature. Evolution has favored this capacity, conserved across species, for the environmental advantages compared to trial-and-error learning. Social group members are critical agents for the learning and development of social and prosocial behaviors. However, whether rodents can acquire prosocial behaviors through observation is not understood. Here, we used a social decision-making paradigm (SDM) in mice in which an observer can learn from a demonstrator how to share a reward with their conspecifics. Following observation, mice displayed a preference for altruistic or selfish choices, without the need for initial training, when they became decision-makers. Observational learning was modulated by demonstrators’ altruistic choices and observers’ prosocial propensity. We then identified neural activation and plasticity changes in the dorsal CA1 (dCA1) that depended on demonstrators’ prosocial behavior. Furthermore, chemogenetic silencing of dCA1 impaired the acquisition of a social preference in mice with high prosocial preference. Fiber-photometry recording also revealed individual differences in hippocampal activity during the observation of altruistic and selfish choices. This study provides a model of observational learning of prosocial behaviors in mice that can be relevant for the study of neuropsychiatric and neurodevelopmental disorders, in which the ability to learn from others’ actions, including altruistic actions, is often compromised, reducing the possibility of forming interpersonal relationships.