The yield properties of about 500 h of outdoor weathering (in the rainy season) of polypropylene (PP) films have been studied. The yield strain, plastic strain, and initial modulus, work of yield attained local maxima at 48- and 240-h exposure time; elastic strain attained near double maxima at these times. The yield stress reached a local minimum for the 144-h exposed film before increasing with further exposure hours. The increase in yield strain, plastic strain, and initial modulus were explained in terms of crosslinking chemocrystallization; decreases were due to chain scission and leaching. Critical dissolution time data, interpreted in proportion to density, crystallite thickness, and percent crystallinity, increased with PP exposure time, reaching a maximum at 48 h before decreasing to values even lower than that of unexposed film from the 120-h exposure.