Lactobacillus fermentum is considered as a beneficial member of the oral normal microbiota. Bacterial aggregation and/or adhesion are essential for their persistence and maintaining the balance in a healthy oral ecosystem. The coaggregation interaction with pathogenic strains is a key factor of the strains to exclude pathogens. The objective of this study was to investigate the environmental factors affecting the adhesion and autoaggregation of oral L. fermentum strains and their coaggregation ability with cariogenic pathogen, Streptococcus mutans. The bacterial cell surface components of these strains were evaluated. The results showed that the adhesion ability of oral L. fermentum to H357 keratinocyte cells was enhanced by cell surface protein, polysaccharides and S-layer protein, while aggregation ability was only mediated by a proteinaceous component. The tested factors including acid-base conditions, calcium ions, sugars and enzymes were analyzed. It was found that the adhesion and autoaggregation of these L. fermentum strains were not inhibited by any tested factors. Moreover, the acidic condition at pH 4.0 and calcium treatment significantly promoted adhesion abilities. Most of the tested factors showed no effect on the coaggregation between L. fermentum and S. mutans, except lactose and lysozyme treatments which decreased this ability. Overall results showed that oral L. fermentum strains had adaptive traits in various factors which were representative of various physico-chemical conditions in the oral cavity.