The ultimate properties of thermally oxidized polypropylene (PP) films have been determined. Attention was focused on the variation of draw stress, tensile strength, draw ratio, breaking extension, breaking factor, work of draw, and work of rupture, with a change in temperature and time of heat treatment. While the draw stress and draw ratio increased with increase in temperature, the tensile strength, breaking extension, work of rupture, and work of draw decreased with increase in temperature. The breaking factor, rather, attained a maximum at 110 degrees C before decreasing with further increases in temperature. The PP films thermally oxidized at 60 degrees C exhibited larger values for the following properties : tensile strength, breaking extension, draw ratio, work of rupture, work of draw, and breaking factor, than for the 100 degrees C oxidized PP films. While breaking extension and tensile strength just decreased with increasing the log time (min), the draw stress, draw ratio, work of rupture, and work of draw were linear functions with negative slopes of log time ( min) of thermal oxidation at a particular temperature. The decrease in all properties studied were explained by decrease in the density of aged PP films.