The microbiome plays a crucial role in odontogenic sinusitis (OS); however, the bacterial characteristics of the sinuses and connected dental regions in OS are poorly understood. In this study, nasal secretion samples were collected from 41 OS patients and 20 simple nasal septum deviation patients, and oral mucosa samples from dental regions were collected from 28 OS patients and 22 impacted tooth extraction patients. DNA was extracted, and 16S rRNA sequencing was performed to explore the characteristics and structure of the microbiome in the sinuses and dental regions of OS patients.The alpha diversity of the oral and nasal microbiomes in OS patients was higher than that in controls. Principal coordinate analysis (PCoA) showed that oral samples clustered separately from nasal samples, and the beta diversity of oral and nasal samples in OS patients was higher than that in controls. The dominant phylum was Bacteroidetes in OS patients and Firmicutes in controls in both the oral and nasal cavity. The dominant genera in the oral microbiome and nasal microbiome of OS patients were similar, including Fusobacterium, Porphyromonas and Prevotella. Co-occurrence network analysis showed decreased microbial connectivity in the oral mucosa and nasal secretion samples of OS patients.Odontogenic infection promotes structural and functional disorders of the nasal microbiome in OS. The interaction of dominant pathogens in the nasal and oral regions may promote the development of OS. Our study provides the microbiological aetiology of the nasal and connected dental regions in OS and is expected to provide novel insights into the diagnosis and therapeutic strategies for OS.© 2023. The Author(s).