Abstract: The heterogeneous bis(cyclopentadienyl)zirconium(IV) dichloride catalyst of the composition MgCl2(THF)/(AlEt2Cl)0.34/(Cp2ZrCl2)0.01 as determined by FTIR, XRD, and AAS analyses was synthesised and, after activation by MAO, applied for ethylene polymerisation. The catalyst turned out to be stable and more active than those magnesium supported catalysts already known from the literature. The polyethylene produced has a relatively high molecular weight (M w >200,000g/mol), a narrow and monomodal molecular weight distribution (MWD=2.4), a bulk density of about 180g/dm3, and monomodal particle size distribution. Application of a ternary Al(i-Bu)3/MAO/B(C6F5)3 activator decreased the amount of MAO needed and increased catalyst activity, but did not change the reaction mechanism. [Copyright &y& Elsevier]