In order to make use of light scattering technique for the determination of molecular weight distribution etc of polymers it is necessary to know the refractive index increment of the system. In this work we have determined the refractive index increment of cellulose acetate in acetone solution. The concentration of the polymer was varied from 1.0 x 10-5 g/ml to 1.0 x 10-1 g/ml. For this purpose two wavelengths of incident light were used. From this data the specific refractive index increment of the system is also determined. To characterize the polymer at different temperatures, we have determined the same parameter at different temperature  (10oC - 55oC) for three different concentrations and making use of three wavelengths of incident light.