Butadiene and styrene were polymerized with the Ziegler-Nattacatalyst system Ni(naph)(2)/Al1.65F1.35. The influence of temperature, monomer, concentration and catalyst concentration on conversion, molecular weight and cis-1.4-content of polybutadiene and tacticity of polystyrene were investigated, Furthermore the copolymerization butadiene/styrene with the same catalyst was realized and the reaction reactivities determined.