Equilibrium and thermodynamics Properties of polystyrene of narrow molecular weight distribution in two chemically distinct good solvents i.e. THF and CCI4 were carried out using static light scattering in dilute solution at 25OC. the molecular weight Mw and radius of gyration Rg for all samples in the range qRp < 1 and qRp 0-2 were obtained using different methods via Zimm, Berry square root and Fujita. It was observed that the molecular weight obtained for the samples 20 x 106  in given solvent by the three graphical procedures are comparable to each other. However, the Rg estimated by the fajita’s are the highest further, it was observed that in case of very high molecular weights (20 x106) samples even the fajita’s method underestimates Rg . this was attributed to the possibility that the chain expansion with increase in molecules with increase the molecular weight is not as uniform as predicted by theory. The second virial coefficients A2 , estimated by Berry square root method were in reasonable agreement with the literature values.