The modified polymers poly(vinyl chloride) differ in their tendency to photo oxidation comparing with that unmodified. It has been studied photostability for modified poly(vinyl chloride) chains using Schiff’s bases derivative of (5-amino-1, 3, 4-thiadiazole-2-thiol) in a manner casting of plastic chips with thickness (40µm) in a solvent Tetrahydrofuran. It has been determined the effectiveness Photostability of these modified polymers through the photodegradation physical measurements for photostabilizer for the modified poly(vinyl chloride).