: Breast cancer (BC) is the leading cause of cancer incidence and mortality among women and the recent identification of a resident mammary microbiota has highlighted its potential role in breast carcinogenesis. Given that environmental and socioeconomic factors influence both BC prevalence and tumor-associated bacterial composition, this study aimed to evaluate the compositional and functional features of the mammary microbiota in cancerous (oncobiome) and adjacent healthy BC tissues from patients living in urban and rural areas. : Microbiota composition in both the oncobiome and adjacent healthy BC tissues was analyzed using 16S rRNA sequencing. : Significant variations in breast oncobiome composition were observed among BC patients from urban and rural areas. A statistically significant β dispersion among breast oncobiome of patients from urban or rural areas was highlighted. Specifically, the genera , , , and were found exclusively in BC tissues of patients from rural areas. Additionally, bacteria from the Neisseriaceae, Porphyromonadaceae, and Selenomonadaceae families, as well as the genus, were significantly enriched in the oncobiome of rural BC patients. Furthermore, the results of the PICRUSt2 (phylogenetic investigation of communities by reconstruction of unobserved states) revealed a significant increase in phospholipid biosynthesis pathways in breast oncobiome of patients from rural areas compared to those from urban areas. : This study provides evidence of distinct compositional and functional differences in the breast oncobiome between BC patients from rural and urban areas. These findings suggest that environmental factors influence local microbiome composition, potentially contributing to BC development and/or progression.