The Rayleigh ratio of toluene at 25 degrees C for a wavelength of 632.8 nm was determined by static light scattering measurement of a certified polystyrene reference material PS 2400 with exactly evaluated or certified mass-average molecular mass (M-w). At first, static light scattering measurements were carried out for PS 2400 in toluene with a literature value of the Rayleigh ratio of toluene. Then, corrections of degree of depolarization, density fluctuations, and molecular mass dependence of refractive index increment were applied to the observed M-w of PS 2400 to obtain apparent M-w. Finally, from the ratio between the apparent M-w, and the certified M the Rayleigh ratio of toluene was reevaluated. (c) 2005 Wiley Periodicals, Inc.