FIELD: chemical industry, technology of organic compounds. SUBSTANCE: invention describes the forming cellulose triacetate composition for processing to films that includes cellulose triacetate, organosilicon block-copolymer as modifying addition and organic solvent. Composition has product of heterofunctional condensation of phenolphthalein-base oligomeric arylate and terephthalic acid chloroanhydride with 
bis-(diethylamino)-oligodimethylsiloxane as an organosilicon block-copolymer where ratio of arylate and siloxane links in blocks is 10-26, value of intrinsic viscosity in tetrachloroethane is 0.055 m3/kg at 20 C in the following ratio of components, wt.%: cellulose triacetate, 8-10; organosilicon block-copolymer, 0.05-0.30 and organic solvent, the balance. Invention provides the effective protection of cellulose triacetate films from photooxidative decomposition, to enhance film light resistance, to decrease amount of macromolecules breaks by some times after UV-irradiation. Invention can be used in production of artificial fibrous and film materials based on complex-mixed cellulose esters. EFFECT: improved quality and properties of composition. 1 tbl
