The thin-film properties of polymeric nanocomposite MEH-PPV/PbS (with PbS quantum dots (QD)) and PbS-QD gamma-irradiated by 0.5–24.4 kGy doses have been studied. The film samples for photoluminescence (PL) investigation were prepared from solution using spin-coating technique, and for photoconductivity measuring were made using slot technique. The threshold doses for irreversible sharp PL-degradation of nanocomposite determined by the degradation of PbS-QD were found. The behavior dynamics of MEH-PPV/PbS photoconductivity after irradiation was analyzed. The conduction relaxation observed in the MEH-PPV/PbS was shown to be due to restoration of damages in the conjugate chains of the MEH-PPV polymer. Moreover, the absence of conductivity and photoconductivity relaxations in the colloidal PbS was revealed.