Effects of the particle shapes and dispersions on the equivalent particle sizes determined by the laser light diffraction pattern analysis are experimentally investigated. The sample model particles are prepared on slide film as photographic images having various shapes (round, rectangular and triangular) and having various concentration (from about 1 to 30%): defined as two-dimensionally dispersed particle images on the film. The results of experimental observation are compared with other equivalent sizes induced from the geometrical dimensions of the rectangular or triangular images. The overlapping effect of diffraction of several particles on the incident beam cross-section is discussed in terms of the particle shape or aspect ratio. This effect determines the light scattering diameter of the non-circular particles.