The polymerization of styrene was mediated by copper (1) bromide/pentramethldiethyltriamine (PMDETA) using ethyl 2-bromopropionate (EBP) as initiator and a catalytic amount of malononitrile (MN) as a novel rate-accelerating additive. The optimal molar ratios of MN/EBP under which the polymerization of styrene can proceed fastest was 4:1. The rate-enhancement-efficiency had a dependence on temperature and the apparent rate constant of polymerization improved by a factor of 2.67 at 85 degrees C. Polymerization resulted in a conversion as high as 87% in 4.3 h in the presence of MN, while a conversion of 79.7% was gained even in 10 h without MN at 85 degrees C. The polymerizations of styrene in the presence of MN proceeded in a living fashion indicated by the first-order kinetic plots, with the increase of M-n with respect to conversion and the relatively narrow polydispersity. The possible rate enhancing mechanism is that the addition of MN weakens the coordination between the copper center and ligand and facilitates the atom transfer process.