The present work consist of two parts:- Part one:-synthesis and characterization Five modified PVC polymers containing benzothiazole and benzimidazole as bending groups in the repeating units were synthesized in this work according to the following: 1-PAA: Reaction of PVC with 2-amino benzothiazole in THF solvent afforded the following modified polymer (PAA) 2-PSS: Treatment of PVC with 2-mercapto benzothiazole in THF solvent under basic condition furnishes the following modified polymer (PSS) 3-PNN: The modified PVC polymer (PNN) was prepared by the reaction of PVC with 2-amino benzimidazole 4-PSA: Reaction of PVC polymer with a mixture of equall amount of 2-amino and 2-mercapto benzothiazole yields the following modified PVC polymer (PSA) 5-PNA: The PVC polymer when treated with a mixture of equivalent quantities of 2-amino benzothiazole and 2-amino benzimidazole afforded the following modified PVC polymer(PNA) Structures of all these modified polymers have been confirmed by spectral (IR,UV) analysis. The results indicated the presence of benzothiazole and benzimidazole rings in the polymeric chain. Part two:-Photostability study The influence of introducing benzothiazole and benzimidazole as a pending groups into the repeating unit of PVC has been studied on the bases of photostability measurements. The photostability of modified polymers were studied by monitoring the carbonyl Index (ICO), polyene index (Ipo) and poly hydroxyl index (IOH), all results obtained indicated that PAA, PSS, PNN, PSA and PNA gave lower growth rate of ICO, IPO and IOH with irradiation time with respect to unmodified PVC film (control) . The following trends of photostability are obtained PAAPSSPNNPSAPNA According to the experimental results several reaction mechanisms were proposed depending on the presence of benzothiazole and benzimidazole moieties in the polymer chain. The kinetic of photodegradation of modified PVC was also investigated and showed the usual kinetic behavior in degradation process, since the linear relation between square root of carbonyl index (ICO)1/2 and irradiation time was obtained. The mode of chain scission was also investigated by measuring the variation of average viscosity molecular weight with irradiation time for modified PVC. The degree of deterioration ( ) and the average number of chain scission (S) values were also calculated.