A new method for simultaneously determining the size and refractive index of epithelial cell nuclei is presented. The function of the modified elastic light scattering spectrum is regarded as a function of wave number factor, Q=2\lambda^-1 sin(\theta/2). The modified spectrum has a constant oscillation period with its frequency proportional to the average diameter of cell nuclei. To the same average diameter, the different relative refractive indexes of epithelial cell nuclei only induce the horizontal shift of the spectra. Both the oscillation frequency and the horizontal shift are quantified by the fast Fourier transform on the modified spectra. The average diameter can be figured out through the peak frequency divided by the value of the refractive index of the surrounding medium. The phase angle of the peak frequency has an approximate linear relationship with the relative refractive index of epithelial cell nuclei.