For both homo- and co-polyacrylonitriles(homo- and co-PAH) prepared in dimethylsulfoxide(DMSO) solution by radical polymerization induced by auto-bis-isobutyronitrile(AIBN), the reaction kinetics was studied. It has been found that the polymerization rate increases with increasing concentrations of moilomer and initiator, and the polymerization temperature. while molecular weight, polydispcrsity. and high molecular-weight-fraction(over 3 $ imes$105 in Mw) decrease.