A method for synthesizing unsupported nickel-tungsten sulfide hydrodearomatization catalysts by breaking SPAN-80 surfactant-stabilized nonaqueous emulsions of solutions of different precursors in dimethyl sulfoxide (DMSO) in situ in a hydrocarbon medium has been first studied using ammonium thiotungstate (NH4)(2)WS4 and 1-butyl-1-methylpiperidinium nickel thiotungstate [BMPip](2)Ni[WS4](2) as precursors and nickel nitrate hexahydrate as a nickel source. The synthesized nickel-tungsten catalysts have been characterized by TEM and XPS. The catalytic activity of the in situ synthesized Ni-W particles in naphthalene hydrogenation has been studied at temperatures of 350-400A degrees C and a hydrogen pressure of 5.0 MPa.