The kinetics of ethylene polymerization with TiCl4/MgCl2/SiO2 has been investigated in the range of temperatures between 40 and 90°C and in the range of ethylene pressures between 4 and 12.4 kg/cm2. The role of MgCl2 was discussed from the dependence of the Mg/Ti ratio on the catalytic activity. The polymerzation rate was first order with respect to the monomer concentration and the dependence of the polymerization rate on the concentration of Al(C2H5)3 could be described by the Langmuir–Hinshelwood mechanism. The dependence of initial rate and the time to reach the maximum polymerization rate on the concentration of Al(C2H5)3 was also discussed. Polymerization rates as a function of the polymerization temperature showed a maximum and the activation energy was 11.8 kcal/mol between 50 and 80°C. The polymerization rate decreased with the increase of hydrogen partial pressure. The active site concentration (C*) was 1.9 × 10−2 mol/mol Ti by the inhibition method with carbon monoxide.