Acrylonitrile (AN) was solution-polymerized in dimethyl sulfoxide (DMSO) and tertiary butyl alcohol (TBA) at 30, 40 and 50°C using a moderate temperature initiator, 2,2′-azobis(2,4,-dimethylvaleronitrile) (ADMVN); the effects of type and amount of solvent, polymerization temperature, and initiator concentration were investigated. On the whole, the experimental results corresponded to predictions. Moderate polymerization temperature using ADMVN proved to be successful in obtaining polyacrylonitrile (PAN) of high molecular weight and high conversion with smaller temperature rise during polymerization. The polymerization rates of AN in DMSO and in TBA were proportional to the 0.61 and 0.94 powers of ADMVN concentration, respectively. For the same polymerization conditions, DMSO was slightly superior to TBA in increasing molecular weight of PAN. On the other hand, DMSO was inferior to TBA in causing conversion to polymer, indicating that the initiation rate of AN in DMSO was less than that in TBA. These effects could be explained by an activation energy difference. For PAN produced in DMSO at 30°C, weight-average molecular weight of 865,000 was obtained, with a polydispersity index of 1.89.