By the application of the Mie and the Rayleigh theories of light scattering to the measurement of specific turbidity, particle size distributions of milled dye dispersions have been determined. The complex refractive index of C. I. Disperse Blue 56 and C. I. Disperse Blue 79 were measured, and extinction coefficients of disperse dyes were calculated. With the increase in milling time and temperature, the specific turbidity in the near-infrared gradually decreases, but increases in the visible range. The specific turbidity method can be utilized in determining the change of the particle size distributions of disperse dyes.