Irradiation of the second harmonics of Nd: YAG laser (532 nm) to gold nano-particles dispersed in gelatin for 5 min changed the diameter of the particles from 10 to 3 nm. At the same time the particles were dispersed more homogeneously after irradiation. Size change was observed with the fluence of more than 90 mJ cm(-2). The particles were dispersed more homogeneously when the number of pulse irradiation increased. Due to the breaking up of the particles, the number density of the particles per unit volume increased 10 times more than that before irradiation.