Abstract: Atom transfer radical polymerization (ATRP) of MMA was investigated using ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate (［Bmim］PF6) and 1-allyl-3-methylimidazolium chloride (［Amim］Cl) as reaction medium. The polymerization of MMA in ［Bmim］PF6 and ［Amim］Cl was formed homogeneous system and heterogeneous system, respectively. Results showed that the reaction in the two ionic liquids all present the linear firstorder kinetic relationship. Conversion and polymerization rate with carbon tetrachloride as initiator were higher than that of benzyl chloride as initiator. ATRP reaction occurred in the phase of ionic liquid in heterogeneous system. PMMA obtained in heterogeneous system presented a narrower molecular weights distribution, but the monomer conversion was lower. FT-IR and 1H-NMR results confirmed that welldefined polymer was obtained in the heterogeneous system, which implied the property of the ionic liquids influenced the polymer structure.