The development of magnetic nanoparticles has gained attention in the field of wastewater treatment but faced several challenges including instability and extremely sensitive to oxidation. Hence, surface modification was generally used as a coating layer of polymer on the surface of magnetic nanoparticles. The present study focuses on the synthesis and characterization of silica-coated iron oxide nanoparticles (IONPs) with different concentrations of IONPs and tetraethyl orthosilicate (TEOS). The IONPs were first synthesized by the co-precipitation method followed by the surface modification of silica on the IONPs through the modified Stober process. The effect of IONPs concentration (1000 mg/L to 10000 mg/L) and TEOS concentration (1 wt% to 10 wt%) was studied through the hydrodynamic particle size and colloidal stability of silica-coated IONPs. The results showed that the IONPs have an average hydrodynamic particle size of 317.53 nm, and zeta potential of -14.33 mV. Besides, it was observed that the increase in the concentration of TEOS and a decrease in the concentration of IONPs lead to nanoparticle agglomeration, thus resulting in large particle size. The optimized concentration of IONPS and TEOS is 5500 mg/L and 5.5 wt%, producing silica-coated IONPS with the smallest particle size (228.23 nm) and high colloidal stability (-20.93 mV).