High activity ethylene polymerization catalysts have been prepared by the reaction of magnesium chloride with titanium tetrachloride in tetrahydrofuran. followed by precipitation with excess n-hexane. The physical properties of catalyst such as surface area and titanium content were measured by BET method and redox titration, respectively. These catalysts were tested with ethylene polymerization reaction in the presence of AlEt3 in the slurry reactor. The activities of prepared catalysts were more than 100kg PE/g·Ti·hr. Kinetic study of ethylene polymerization was performed by varying catalyst concentrations, monomer concentrations, the Al/Ti ratios, polymerization temperatures and hydrogen pressures. The overall polymerization rate was found to be first order with respect to the monomer concentration and the number of active sites. The decay rate of active sites was found to be first order with respect to time. The activation energies of propagation and the decay reaction of active sites were found to be 5.73 and 4.00 kcal/mol, respectively.