Ethylenebis(5-chlorosalicylideneiminato)vanadium dichloride supported on MgCl2(THF)(2) or on the same carrier modified by EtnAlCl3-n, where n = 1-3, was used in ethylene polymerization in the presence of MAO or a common alkylaluminium compounds as a cocatalyst. The support type alter vanadium loading and also change the characteristic of the catalytic active sites. Et2AlCl is the best activator for a catalyst which has been immobilized on a nonmodified support, whereas the systems which contain a carrier which has been modified by an organoaluminium compound reveal the highest activity in conjunction with MAO. That difference, together with different temperature effects on polymerization efficiency (i.e., decrease and increase of catalytic activity for increasing temperatures, respectively) suggest the formation of different types of active sites in the catalytic systems supported on modified and nonmodified magnesium carrier. However, all supported precatalysts possess a long lifetime, still being active towards ethylene polymerization after 2 h. All the systems yield wide MWD polyethylene, while bimodal MWD is found for some part of analyzed samples. Polyethylene with bimodal particle size distribution is formed with the system which contain modified carriers at higher temperatures. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3480-3489, 2009