Catalytic emulsion polymerization of ethylene with nickel catalysts in the presence of silica nanoparticles affords stable dispersions of silica/polyethylene. nanocomposite particles. The modification of the surface of silica particles by grafting upon their surface of octenyl-or octylsilanes is a prerequisite for obtaining composites. Different morphologies of composites particles were observed depending on the microstructure and crystallinity of the polyethylene part, controlled by different catalyst precursors. Composite structures consisting of silica spheres at the surface of lentil-like crystalline polyethylene particles were formed with a nickel(II) phosphinoenolate catalyst precursor or with the Ni(II) salicylaldiminato complex [{kappa(2)-N,O-6-C(H)=NAr-2,4-I2C6H2O}NiMe(tmeda)] (Ar=2,6-{3,5-(F3C)(2)C6H3}(2)C6H3). In contrast, silica particles homogeneously embedded in an amorphous polyethylene matrix are observed by TEM when another Ni(II) salicylaldiminato catalyst precursor (Ar = 2,6-{3,5-Me2C6H3}(2)C6H3) was used in the presence of a copolymerizable octenyl-modified silica.