BACKGROUND/AIM: Host microbiota dysbiosis has been recognized as a key factor in lung cancer. However, the specific diversity and composition of microbiota in lung cancer patients remain unknown. This single-center prospective observational study analyzed both saliva and fecal samples from 74 participants [lung cancer (LC) patients: n=53; lung inflammation (LI) patients: n=11; healthy control (HC): n=10]. PATIENTS AND METHODS: We performed 16S ribosomal RNA gene sequencing and analyzed the associations between oral and gut microbiota diversity and composition across the three groups. RESULTS: Alpha diversity of the oral microbiota was significantly lower in the LC group than in the HC group (Chao 1, p=0.004; Simpson, p=0.018; Shannon, p=0.009). Beta diversity of both oral and gut microbiota showed significant differences among the three groups (PERMANOVA, oral: p=0.005; gut: p=0.002). Compositional differences in the oral microbiota were observed between the HC and LC or LI groups; in particular, Bacilli class, Streptococcaceae family, Streptococcus genus, Firmicutes phylum, and Lactobacillales order were more abundant in the LC group. Additionally, six oral-related microbiota showed significant abundance in the gut of the LC group (p=0.00182). CONCLUSION: The oral microbiota in lung cancer patients is significantly different from that in healthy individuals. Specific changes in oral microbiota and oral-related gut microbiota compositions were evident in lung cancer patients. These findings might be useful for identifying novel biomarkers to predict the risk of lung cancer and prevent the disease.