The effect of aqueous detergent and benzine washing on the photo-oxidation stability of stabilized polypropylene fibers was studied. The fibers were stabilized by higher molecular weight light stabilizers based on 2-hydroxybenzophenones and by thermo-oxidative stabilizers. The content of the light stabilizers in washed fibers was determined, and photo-oxidation curves of the original and washed fibers were measured. The effectiveness of stabilization of the original and the washed fibers was compared with that of 2-hydroxy-4-n-octyloxybenzophenone at identical content of 2-hydroxybenzophenone structural units. Another criterion was comparison of washed and unwashed fibers. Photo-oxidation curves of accelerated aging and induction periods showed that washing with either aqueous detergent or benzine decreases the resistance of fibers to photo-oxidation, i.e., washing lowers the content of stabilizers in fibers. Extraction with benzine exerts a more pronounced effect than washing with water. Extractability by benzine of higher molecular weight stabilizers is considerably lower than with low molecular weight stabilizer. On the basis of experimental results it is assumed that washing of fibers leads to leaching not only of thermo-oxidative stabilizers but also to a decrease in the content of light stabilizers. Derivatives alkylated by tert-butyl are more extractable by benzine, while the nonalkylated derivatives are more extractable by washing with water.