In this work polyvinyl acetate prepared by B. D. H Laboratory »Chemicals Di- vision has been used. The intirinsic viscosities have been determined in acetone-benzene mixtures of various percentâges. By using these intrinsic viscosity values the viscosity average molecular weights of the same polyvinyl acetate sample have been calculated from this relationship: [?]] = K' M»' (1) In this equation the values of K and a' are calculated from the following equations: K' = — Ki (1—fi)3 + K2 (1—fi)3 (2) a' = «ı fi + a2 ( 1—fı) (3) Where fi stands for the volüme fraction of one solvent in the solution. Kn aı and K2, a2 are constants for a given polymer-solvent system and temperature. The values of Kn aı and K2, a2 are given in the literatures [1, 2 ] for polyvinyl ace- tate-benzene and polyvinyl acetate-acetone systems. The values of the molecular weight abtained by this method are satisfactorily good within experimental errors. The benzene-acetone mixture is better than püre ben¬zene and acetone as solvent for the polyvinyl acetate. Especially the solution containing 20-40 % benzene is the most effective solvent for this polymer. Here polar and nonpolar parts of the polymer are respectively affected by acetone and benzene.