The effects of butyl chloride as a promoter in the ethylene polymerization were studied using a Mg(OEt)2/TiCl4/triethyl aluminum (TEA) Ziegler–Natta catalyst system, where Mg(OEt)2, TiCl4, TEA were used as support, catalyst, and activator, respectively. The influence of BC on the catalyst performance, polymerization rate, and polymer properties were investigated. This study strongly indicates that BC could act as a promoter with high performance in the ethylene polymerization. There was a remarkable increase in the catalyst yield and polymerization rate, in particularly, in the presence of hydrogen which was used for controlling the molecular weight. A reduction in the polymer molecular weight was observed in the presence of BC and hydrogen. The morphology of the polymers was evaluated through scanning electron microscopy and particle size distribution. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40189.