Autism spectrum disorders are potentially associated with gastrointestinal dysfunction, although the underlying mechanisms remain unclear. Recently, the oral cavity has gained attention as the starting point of the digestive tract. We aim to explore the potential association between altered oral microbiota and oxidative stress in individuals with autism spectrum disorders. We conducted a case-control study involving 54 subjects with autism spectrum disorders and 46 typically developing participants. Oral epithelial cells and saliva samples were collected to analyze oxidative stress markers and oral microbiota composition using 16S rDNA sequencing. Compared with typically developing participants, individuals with autism spectrum disorders exhibited suppressed mRNA levels of superoxide dismutase 2 and RAR-related orphan receptor a, increased H3K9me2 modifications at superoxide dismutase 2 promoter, elevated levels of 8-oxo-dG in oral epithelial cells, and a reduced ratio of reduced glutathione/oxidized glutathione (GSH/GSSG) ratio in saliva. In addition, alpha and beta diversity analyses showed significant differences in microbial richness, evenness, and intersample variation between the autism spectrum disorder and typically developing groups. Statistical analyses confirmed marked distinctions in microbial diversity and community structure between the two groups. Individuals with autism spectrum disorders show increased oxidative stress and altered oral microbiota compared with typically developing participants. While the underlying mechanisms remain unclear, these findings suggest that altered oral microbiota may be linked to oxidative stress, providing insights into autism spectrum disorder pathology and potential avenues for clinical intervention.