Abstract: There is a great deal of natural bacteria in the human oral cavity. Dental plaque biofilm is a major exsiting form of bacteria. Plaque biofilm, which is the primary etiological agent in dental caries and periodontitis, has many metabolic and physiological characteristics obviously differing from the state of the planktonic bacteria. This article introduced the characteristics about several major oral pathogenic bacteria in biofilm and planktonic condition such as susceptibility to antimicrobial agents, gene expression, signal conduction and acid tolerance and
so on.