The light scattering method applicable for the soot particle measurements in transient flames was developed. The method was applied for the soot particle measurements in steady and non-steady propane diffusion flames.A 4W horizontal polarized Ar ion laser emitting multiple radiations is used as the light sourse. The wavelengths used for the measurements are the 488.0nm and 514.5nm, and those scattered intensities are measured at fixed angular positions of γ=60° and γ=120° with the photomultiplier tube, respectively, (γ is the angle between the direction of observation and inverse direction of the incident light beam.)The diameter of soot particle can be determined from the ratio of both intensities. The number density can be determined from the calibrated value of latex-distilled water system.Experiments were made in latex-distilled water system, static and intermittent flames of steady flow and non-steady flame. A detailed comparison of results of conventional method (polarized light ratio) and this method were discussed and appropriated.