A non-negative least square (NNLS) algorithm was applied to inversion computation of particle size distribution in photon correlation spectroscopy. Four mono-disperse particle samples were measured by NNLS
and the results were compared with those measured by the instrument of Brookhaven Company and the nominal diameter of the samples. The comparative results show that the non-negative least square algorithm works precisely on inversion computation of the diameter and size distribution of mono-disperse particles.