We have synthesized a series of nanocatalysts with different sizes (50-200 nm) for polymerization of 1,3-butadiene (Bd) by immobilizing salicylaldimine cobalt complexes on the mesoporous silica nanoparticles (MSNs). The prepared catalysts have been characterized by infrared (IR) spectra, thermal gravimetric analyses (TGAs), chemical composition analysis, nitrogen adsorption-desorption, scanning electron microscope (SEM), and transmission electron microscope (TEM). The nanocatalysts in combination with methylaluminoxane (MAO) show excellent catalytic efficiency in polymerization of 1,3-butadiene. The results reveal that these nanocatalysts also show higher activity than the homogeneous analog of cobalt complex and the same catalyst on bulky mesoporous silica supporting materials. The yield and the molecular weight of the poly-butadiene product depend on the particle size of the catalyst support. This catalysis process is also a facile way to directly synthesize the polymer/silica composite materials.