We report the synthesis of cobalt nanoparticles (Co NPs) via a DMF-protecting method and their use as catalysts in hydrosilylation reactions. Various types of cobalt nanoparticles were synthesized from different precursors, namely, cobalt(II) acetate, cobalt(III) acetylacetonate, and cobalt(II) bromide, to give Co NPs-OAc, Co NPs-acac, and Co NPs-Br, respectively. A range of methods, e.g., annular dark-field scanning transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption fine structure, were used to investigate their chemical properties. The results indicated that these cobalt nanoparticles involved a structure of Co