High-density polyethylene films were treated with chromic acid mixture at 70°C. The treated films were then reacted with 2,4-Dinitrophenylhydrazine. The changes in the amounts of carbonyl groups and 2,4-dinitrophenylhydrazones formed in the films were estimated by comparing their absorptions in the infrared and ultraviolet spectra, respectively. Scanning electron micrographs of the treated film surfaces were taken. Oxidation of the film surface zone, etching of the film surface zone, and oxidation of surface zone bared from the film inner zone seem to have occured with increase in treatment time. High-density polyethylene film surfaces were oxidized to a greater extent than low-density polyethylene film surfaces; however, the rate of etching of the low-density polyethylene film surface zone was larger than that of the high-density polyethylene film surface zone.