Inferring the beliefs, desires, and intentions of other people (?theory of mind,? ToM) requires specialized psychological processes that represent the minds of others as distinct from our own [1?3]. ToM is engaged ubiquitously in our everyday social behavior and features a specific developmental trajectory [4] that is notably delayed in children with autism spectrum disorder (ASD) [5, 6]. In healthy individuals, model-based analyses of social learning and decision-making have successfully elucidated specific computational components of ToM processing [7?11]. However, the use of this approach to study ToM impairment in ASD has been extremely limited [10, 12]. To better characterize specific ToM impairment in ASD, we developed a novel learning task and applied model-based analyses in high-functioning adults with ASD and matched healthy controls. After completing a charitable donation task, participants performed a ?mentalizer? task in which they observed another person (the agent) complete the same charity task. The mentalizer task probed the participants? ability to acquire and use ToM representations. To accurately predict agent behavior, participants needed to dynamically track the agent?s beliefs (true or false) about an experimental context that varied over time and use that information to infer the agent?s intentions from their actions. ASD participants were specifically impaired at using their estimates of agent belief to learn agent intentions, though their ability to track agent belief was intact and their reasoning about belief and intentions was rational. Furthermore, model parameters correlated with aspects of social functioning, e.g., ADOS severity scores [13]. Together, these results identify novel, and more specific, targets for future research.