The effective immobilization and activation of a single-site chomium catalyst for ethylene polymerization has been achieved using MgCl2/AlRn(OEt)(3-n) supports, without the use of methylaluminoxane (MAO) or a borate activator. High catalyst activity and a spherical polyethylene-particle morphology is obtained. Furthermore, the single-site characteristics of the catalyst are retained, the narrow molecular weight distribution of the polymers obtained are apparent from gel permeation chromatography.