he microscopic molecular structure of a poly (methylmethacrylate)(PMMA) Langmuir-Blodgett (LB) monolayer was studied by Atomic Force Microscopy (AFM). An AFM image of a PMMA monolayer on highly oriented pyrolytic graphite (HOPG) indicating that the alignment direction of the backbone of PMMA is parallel to the barrier surface and vertical to the deposition direction of the LB films was observed for the first time. The area per PMMA unit obtained from AFM images fits well with that from -A curves of PMMA Langmuir films. Then the description of PMMA LB films performed process was given and reasons of PMMA backbone alignment were discussed. By means of AFM images

another case of PMMA monolayer which is on silic (Si) substrate was shown to have the helical coiling of PMMA chains. Reasons for this phenomenon are suggested.