Poly(methyl methacrylate) (PMMA) samples of molecullU" weight 6.49xl04 ­12.68xlO" were investigated for their intrinsic viscosity, unperturbed chain dimension and chain expansion parameters in acetone and acetonitrile in the temperature rangelO°. 4O"C. MlIIk-Houwink's constants 'K' and 'a' lU"e determined for the systems the data show that the 9 temperature for PMMA-Acetonitrile system is round about 35"C. Ke values have been predicted from various theoretical models and complU"ed with experimental values, on the basis of which Ahmad-Baloch (AB) model is regarded as best for the theta solvent and Stockmayer­Fixman (SF) model for the good solvent. Using purely viscosity data radius of gyration (Rc> and expansion factor 'a' have also been calculated for both the systems and has been discussed.