The Morphology of crazes in ultrathin film of poly (methyl methacrylate) prepared by evaporation from different concentration solutions has been observed by TEM. The craze morphology was affected strongly by casting concentrations.When concentration was either too low or too high

only homogeneous deformation zones (DZs) were observed

whose microstructure with their inner microvoids were different from each other. When concentration was within the proper range

both crazes and DZs were observed. With the concentration increasing

the mechanical properties of film were improved. It could also be concluded that fibrillar ceazes initiated in the deformation zones

and the microfibril breakdown took place in the middle of its fibril.