Atomic force microscopy (AFM) has been used for the characterization of the surface topography and microstructure of polyethylene (PE) films with thickness of about 50 μm. Different compositions of the films were tested, including mixtures of LDPE fabricated with metallocene polyethylene (mPE). The characteristics of the fibrils and spherulites of the films have been observed by means of AFM without any preparation of the samples, allowing also differentiation of the amorphous and crystalline zones. A method is proposed for the quantification of the proportion of crystallinity based on the roughness of the films.