Radical polymerization of acrylonitrile initiated by azobisisobutyronitrile under various conditions with or without magnetic field (MF) has been conducted. The polyacrylonitrile (PAN) prepared under MF is found to be of higher molecular weight, narrower polydispersity, higher tacticity and higher thermal stability than those of PAN prepared without MF. On heating, PAN prepared under MF results in higher char yield due to higher degree of cyclization of chain augmented by the greater degree of tacticity. All these effects increase with the strength of MF used for polymerization.