The preparation of a polymer with both low polydispersity and high tacticity is one current challenge we face and warrants thorough investigation from both the theoretical and experimental standpoints. In this study, we synthesized polyacrylonitrile (PAN) with simultaneously controlled molecular weight and tacticity on the basis of the strategy of the atom transfer radical polymerization (ATRP) of acrylonitrile (AN) in the presence of Lewis acids. A new combined initiation system of 3-bromopropionitrite (3-BPN)/Cu2O/N,N,N',N'-tetramethylethylenediamine (TMEDA) was used for the ATRP of AN for the first time. When the polymerization was performed with the ratio [An](0)/[Initiator](0)/[Cu2O](0)/[TMEDA](0) = 190/1/0.5/1.5 (where the subscript 0 indicates the initial conditions) in ethylene carbonate at 60 degrees C for 48 h, the polydispersity of the obtained PAN was 1.13, and the molecular weight was up to 13,710. The polymerization kinetics results show that the polymerizations proceeded with a living/controlled nature except that an induction period existed during the polymerization process because of the lower initiating activity of 3-BPN. Also, two kinds of Lewis acid, AlCl3 and yttrium trifluororomethanesulflnate, were used in the ATRP system of AN for the tacticity control. The addition of 0.01 equiv (relative to AN) of the Lewis acid AlCl3 in the polymerization afforded PAN with an improved isotacticity [meso/meso triad (mm) = 0.321 and a very narrow polydispersity (1.06). (c) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 2610-2616, 2010