Children differentiate and diversify their lexicons and syntactic structures when interacting with different interlocutors to improve mutual understanding. Autistic children may not be able to adapt language features as flexibly as their typically developing (TD) peers, resulting in challenges in expressing intentions effectively. Thus far, there is limited evidence on the language diversity of autistic children when interacting with interlocutors of different familiarity levels, particularly in online conversations. This study examined the effects of interlocutor familiarity on the lexical and syntactic diversity of 10 Malaysian English-speaking autistic children aged 6-8 years old in online conversations. Each child interacted with their mother (familiar interlocutor) and an undergraduate student (unfamiliar interlocutor) through a 10-minute online role-play game. Using CLAN software, the children’s lexical diversity was computed using Voc-D and syntactic diversity using the Index of Productive Syntax (IPSyn) subscales. Our analysis showed that the lexical and syntactical diversity of autistic children is not influenced by interlocutor familiarity. This study’s findings are preliminary and have implications for informing scaffolding strategies in online contexts.