This study tested the role of children with autism spectrum disorder (ASD)'s conversational expansion in mediating between mothers' descriptive language and children with ASD's conversational repair, and whether this mediation was moderated by the relative complexity of mother-child language. Videos of forty children with ASD engaging in various activities with their mothers were transcribed into language samples and then coded. Mediation analyses indicated that conversational expansion mediated the association between descriptive language and conversational repair. Moderated mediation analysis further indicated that the relative complexity of mother-child language moderated the relationship between descriptive language and conversational expansion, creating a conditional indirect effect. Although preliminary, the results of this study provide parents and practitioners with a new idea of language intervention strategies.