Background and aims Peer-mediated interventions (PMIs) are effective strategies to foster socialization of children with autism spectrum disorder (ASD) in natural settings. However, research examining the efficacy of peer mediation for students with ASD who have the greatest cognitive and language impairments remains limited. Additionally, previous studies essentially targeted communicative abilities of participants. To address this gap, the present study evaluated the effects of a play-based PMI on three socio-communicative skills (play, social engagement and imitation) of minimally verbal students with ASD who also have a comorbidity of intellectual disability (ID). Methods Seven children with ASD attending ordinary school settings and 14 typically developing (TD) preschoolers participated. Seven single-sex groups were formed, and children played together during two 30 min weekly sessions. TD children were trained according to the principles of the integrated play group model. We used a multiple-baseline design across participants to measure the effects of the intervention on play skills, social engagement and motor imitation of students with ASD. Results Outcomes revealed an intervention effect for most of the participants, despite some variations across children. After the peer training, four children increased their duration of functional/symbolic play, six children improved their duration of interactive play and five children increased their rates of motor imitation. Concerning maintenance gains, inter-individual differences are also important. Conclusions and implications These findings suggest that a play-based PMI may be a feasible option for targeting inclusive education and improving socio-communicative skills of some minimally verbal students with ASD who also have an ID. However, variations across children invite further research to clarify how individual factors can moderate the effects of PMIs in children with ASD who are the most impaired.