Oil in water microemulsion containing soybean oil and egg phosphatide was prepared by vacuum high shear mixing and high pressure homogenizing. The laser particle sizer, Coulter counter and photomicroscope were used to determine the particle size distribution at each cycle of homogenizing. Particularly, the laser particle sizer(dynamic light scattering method) was applied to the study of particle size distribution behavior below $1;{mu}m$. It was found that the particle size distribution below $1;{mu}m$ was shifted to lower size range as the number of passing cycle was increased. Beyond the 7th cycle, however, the particle size distribution was not varied.