Bio-composites with vegetal reinforcement have experienced great industrial development in various sectors of activity such as: automotive, electronics, medical, or construction. Compared with synthetic fibers, plant fibers have numerous environmental, technical, processing, economic and health advantages. With the objective of application in the dental field, we present in this paper the study of bacterial adhesion on a biomaterial composite with polypropylene reinforced vegetable fibers extracted from the Alfa plant (stepa tenassicma).For this study, two strains of bacteria from the oral bacterial flora were chosen, Lactobacillus acidophilus and Streptococcus mutans, and analyzed by spectrophotometric method.The results analysis shows clearly the formation of biofilm by bacterial adhesion is remarkable in the presence of the composite not reinforced by vegetable fibers in comparison with the biocomposite reinforced by Alfa fibers, and more remarkably formed by the strain Streptococcus mutans than with the strain Lactobacillus acidophilus.