After a proper modification of a commercial Coulter LS230 particle size analyzer that is based on Fraunhofer principle, we have developed its novel application in directly sizing particles dispersed inside a solid matrix. Using several particle standards, we have demonstrated its validity by comparing the particle size distributions, respectively, obtained in water and directly inside different solid matrixes. Ln comparison with other conventional sizing methods, such as transmission electron microscopy (TEM) and scanning electron microscopy (SEM), this novel application of Fraunhofer diffraction provides a fast, convenient, and direct way to characterize particles dispersed inside a transparent or translucent solid matrix. It can be envisioned that this application can be extended to directly size fillers inside a polymer materials, microdomains inside a polymer blends, and bubbles inside a foam.