The results of study of ethylene oligomerization in the presence of complex catalysts based on mixed-ligand beta-diketonatozirconium chlorides acre presented. The influence of the composition of a zirconium compound, the electron affinity of beta-diketonate ligands, component ratio of the catalytic system, temperature of the process, solvent nature, and other factors on the catalyst activity and molecular-mass distribution of the product of ethylene oligomerization was studied.