Measurements of dynamic light scattering along with classical scattering/extinction as a function of the wavelength for a rich propane/oxygen flame are presented. Spectral optical properties of soot particles are inferred in the visible and infrared part of the spectrum. Particle size distribution. number densities and volume fractions of soot are determined and comparisons are made with predictions of existing models for the soot optical constants. The effects of agglomeration and temperature in the determination of the optical properties are assessed and a new set of dispersion constants for the optical properties of flame soot is presented.