The photostabilization of poly(vinyl chloride) (PVC) films by 2N-salicylidene-5-(substituted)-1,3,4-thiadiazole compounds was investigated. The PVC films containing concentration of complexes 0.5% by weight were produced by the casting method from tetrahydrofuran (THF) solvent. The photostabilization activities of these compounds were determined by monitoring the carbonyl, polyene, and hydroxyl indices with irradiation time. The changes in viscosity average molecular weight of PVC with irradiation time were also tracked (using THF as a solvent). The quantum yield of the chain scission (phi(cs)) of these complexes in PVC films was evaluated and found to range between 4.72 x 10(-8) and 8.99 x 10(-8). Results obtained showed that the rate of photostabilization of PVC in the presence of the additive followed the trend: SN > SC > SB > SI > SP According to the experimental results obtained, several mechanisms were suggested depending on the structure of the additive. Among them, UV absorption, peroxide decomposer, and radical scavenger for photostabilizer mechanisms were suggested. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 2207-2214, 2011