Background: Children with autism spectrum disorder (ASD) are impaired in social communication and interaction with peers, which may reflect diminished social motivation. Many children with ASD show enhanced stress when playing with other children. This study investigated social and stress profiles of children with ASD during play. Methods: We utilized a peer interaction paradigm in a natural playground setting with 66 unmedicated, prepubertal, children aged 8-12 years [38 with ASD, 28 with typical development (TD)]. Salivary cortisol was collected before and after a 20-min playground interaction that was divided into periods of free and solicited play facilitated by a confederate child. Statistical analyses included Wilcoxon rank-sum tests, mixed effects models, and Spearman correlations to assess the between-group differences in social and stress functioning, identify stress responders, and explore associations between variables, respectively. Results: There were no differences between the groups during unsolicited free play; however, during solicited play by the confederate, significant differences emerged such that children with ASD engaged in fewer verbal interactions and more self-play than the TD group. Regarding physiological arousal, children with ASD as a group showed relatively higher cortisol in response to social play; however, there was a broad range of responses. Moreover, those with the highest cortisol levels engaged in less social communication. Conclusions: The social interaction of children with ASD can be facilitated by peer solicitation; however, it may be accompanied by increased stress. The children with ASD that have the highest level of cortisol show less social motivation; yet, it is unclear if it reflects an underlying state of heightened arousal or enhanced reactivity to social engagement, or both.