Polystyrene (PS) and cellulose triacetate (CTA) as well as their mixts. were exposed to short-wavelength UV-irradn. (253,7 nm) and subjected to action of microorganisms present in an activated sludge. The changes in structure of polymers were monitored by FTIR and UV-Vis spectroscopy as well by gel permeation chromatog. The amt. of crosslinked gel was estd. by gravimetry. Photooxidative degradn. of PS and its blends with CTA was obsd. The addn. of CTA to PS matrix enhanced its susceptibility to biodegrdn.