This study is concerned with the cololymerization of acrylonitrile(AN) with methyl acrylate(MA) and itaconic acid(IA) using the sodium sulfite/sodium chlorate initiator in zinc chloride($ZnCl_{2}$) aqueous solution. In the free radical polymerization in $ZnCl_{2}$ aqueous solution, the rate of polymerization increases linearly with increasing monomer concentration. The extent of conversion increases almost linearly with increasing polymerization time at the monomer concentrations of 8.0 wt%, 10.0 wt%, 12.0 wt% and 13.0 wt%, whereas an abrupt increase in the conversion rate is observed at higher monomer concentrations. In fact, the polymerization process at monomer concentrations higher than 13.0 wt%, was very difficult to control because the extensive exothermic polymerization reaction accelerates the polymerization reaction. This indicates that a self acceleration and irregular chain transfer reactions take place during polymerization. Thus, the number average degree of polymerization decreases with monomer concentration. It was found that the optimum concentration of monomer was 10.0∼12.0 wt%. On the other hand, the limiting conversion increased with increasing monomer content.