Aim: The purpose of this study was to investigate the effect of oxidative stress on physiological and genetic characteristics of Fusobacterium nucleatum and its interference on this microbial identification methods. Methods and Results: Fus. nucleatum ssp. nucleatum ATCC 25586 (wt-strain) and an oxidative-stress-adapted strain derived from the wt-strain (aero-strain) were employed in the study. Cell-free crude protein extracts were obtained from both strains and differentially expressed proteins were identified by two-dimensional electrophoresis. Bacterium identification was performed by conventional biochemical tests, automated Rapid ID 32A system and specific PCR analysis. Genetic diversity between wt- and aero-strain was assessed by arbitrarily-primed (AP)-PCR. There were significant changes in the protein profile of aero-strain. The identification of the wt-strain was confirmed by all methods employed. Similar results were obtained for aero-strain when conventional biochemical tests and PCR were used. However, aero-strain was identified as Fusobacterium varium when submitted to Rapid ID 32A system. According to AP-PCR analysis, no significant genetic alteration was detected in aero-strain. Conclusions: The adaptive response of Fus. nucleatum to oxidative stress is associated with changes on its biology, which may lead to misidentification of the organism, according to the conventional identification methods. Significance and Impact of the Study: Oxidative stress may act as a cause of adaptive response in Fus. nucleatum with consequences to its biology, such as alterations on biochemical and physiological profile.