Self-assembly is one of the few practical methods for fabricating nanostructures. Currently, the fabrication of a nanostructure is determined by the initial conditions such as temperature, concentration of the particle, pH balance, etc. In order to precisely fabricate nanostructure devices using self-assembly, it is necessary to use real-time controlling, which is based on in-situ evaluations. In this study, we have proposed an in-situ particle sizing system to visualize interactions between nanocomponents. The system uses two particle sizing methods to cover a range of particle diameters. In the first method (for diameters of 1-10 nm), particle sizes are evaluated from the rotational diffusion coefficient of Brownian motion using fluorescence polarization. In the second method (for diameters of 10-500 nm), particle sizes are evaluated from the diffusion coefficient of a particle tracking method. The system can be integrated into a fluorescence microscope with a particle tracking system. We constructed an optical system and a particle sizing system and evaluated their properties.