The fine structure of the cell walls of Gram-positive and -negative bacteria were determined by electron microscopy with the new technique of freeze substitution method, and analysed the cell wall structure of Staphylococcus aureus in detail. The surface of Staphylococcal cell wall was covered with a fuzzy coat consisting of fine fibers or electron-dence mass. This coat was completely removed after extraction of teichoic acid from the cell wall with trichloroacetic acid treatment, but was not affected by sodium dodecyl sulfate or trypsin treatment. It was suggested that many amount of teichoic acid was located on the surface of the cell wall and less inside the cell wall. The capsule of strain Smith diffuse was assumed to play the role as the barrier protected from the penetration of antibody against teichoic acid.