The kinetics of methyl methacrylate (MMA) homopolymerization performed by atom transfer radical polymerization (ATRP) is investigated in detail using ethyl-2-bromopropionate (EPN-Br) as initiator, CuBr as catalyst, and pentamethyldiethylenetriamine (PMDETA) as ligand in ionic liquids (ILs) and acetonitrile. ILs in this research covered two different substitutional imidazolium cations and anions including halogen and halogen-free ones. The typical cations include 1-butyl-3-methylimidazolium, 1-ethyl-1-3-methylimidazolium and the typical anions include bromide, tetrafluoroborate. The effects of solvents, temperature, and reaction ingredients ratios on the polymerization kinetics are all investigated in this article and the apparent energy of activation (Delta E-a(app)) calculated for the ATRP of MMA in 1-butyl-3-methylimidazolium tetrafluoroborate is 6.95 KJ/mol. The number-average molecular weights (M-n) increase linearly with conversion but are Much higher than the theoretical values. It is probably due to the low concentration of deactivator at the early stage of polymerization and the lower bond energy of C-Br in PMMA-Br than that in EPN-Br. Moreover, the catalyst is easily separated from the polymer and the regenerated catalyst is reused for more than three times. (C) 2008 Wiley Periodicals, Inc.