The photostabilization of poly(methy methacrylate) (PMMA) films by 2-thioacetic acid benzothiazol with Sn(II), Cd(II), Ni(II), Zn(II) and Cu(II) complexes was investigated. The PMMA films containing concentration of complexes 0.5% by weight were produced by the casting method from chloroform solvent. The photostabilization activities of these compounds were determined by monitoring the hydroxyl index with irradiation time. The changes in viscosity-average molecular weight of PMMA with irradiation time were also tracked (using benzene as a solvent). The quantum yield of the chain scission (Φcs) of these complexes in PMMA films was evaluated and found to range between 3.64 × 10−5 and 7.44 × 10−5. Results obtained showed that the rate of photostabilization of PMMA in the presence of the additive followed the trend: Ni(L)2>Cu(L)2>Zn(L)2>Cd(L)2>Sn(L)2 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 additives mechanisms were suggested.