This paper investigated the determination of critical coagulation concentration using a time-resolved dynamic light scattering technique. Silicon nanoparticles were used as model nanoparticles. Zeta potential of silicon nanoparticles were quantified using a zetasizer. The key results of this study show that critical coagulation concentration of silicon nanoparticles in NaCl is 0.2 M while critical coagulation concentration decreased to 0.01 for CaCl2 solution. This finding indicates that silicon nanoparticles are less stable in CaCl2 because of the more effective surface charge screening process occurred. This study provides information on the stability of nanoparticles in electrolyte solutions and may be served as reference in the risk assessment of nanoparticle spills into the natural aquatic systems.