The effect of some plant gums on the polymerization of acrylonitrile (AN) using ceric ammonium nitrate (CAN) as an initiator in the presence of air (containing 21% oxygen) was studied. The induction period and percent conversion were determined. The induction period in the presence of gum was comparatively lower than that under a N-2 atmosphere. The rate of polymerization has a 1.5-power dependence on the monomer concentration and the rate is sufficiently high at moderate temperature. The rate also increased with an increasing initiator concentration and reaches a maximum value of 93% at 0.72 x 10(-2) mol L-1 of CAN. The activation energy was found to be 6.4 kcal mol(-1). Both the molecular weight and density of the polyacrylonitrile (PAN) prepared in the presence of gum were higher than those of PAN prepared in the absence of the gum. The PAN produced in the presence of the gum was thermostable than that prepared in its absence.