While tobacco smoking is a risk factor in the development of oral squamous cell carcinoma (OSCC), only a fraction of smokers develop the disease. Compelling evidence shows that microbial community composition is associated with carcinogenesis, suggesting that the microbiome may play a role in cancer development of smokers. We previously showed that black raspberry (BRB) protects against OSCC induced by the tobacco constituent dibenzo[def,p]chrysene (DBP) via alteration of genetic and epigenetic markers in a manner consistent with its cancer preventive activity. In the present study, we conducted a mouse experiment to investigate the effects of BRB and DBP individually and in combination on the oral and gut microbiota. DBP-induced DNA damage in the mouse oral cavity is an essential step for the development of OSCC in mice. 16S rRNA gene sequencing revealed that BRB significantly increased microbial diversity and shifted microbiome composition in the gut and oral cavity, whereas DBP had no significant effect. In both gut and oral microbiota, Akkermansia muciniphila was significantly reduced after BRB treatment; however, this was not consistent with pure culture in vitro assays suggesting that the impact of BRB on A. muciniphila may be mediated through indirect mechanisms including the host or other microbes. Indeed BRB, but not DBP, was found to modulate the growth kinetics of human gut microbes in vitro including lactic acid bacteria and Bacteroides spp. The results of the current study further emphasize the interplay of microbiome and environmental factors in the development and prevention of OSCC. Prevention Relevance: Our work clearly demonstrates the modulatory impact of BRB on both gut and oral microbiomes within a DBP-induced OSCC mouse model and paves the way for future research examining a causal role of BRB-microbiota interactions at different stages of disease progression.