The copolymerization behaviour of N-vinylpyrrolidone (NVP) and methyl methacrylate (MMA) in the presence of ZnCl2 was investigated. It was observed that, the value of the mono- mer reactivity ratio at 65 °C for NVP (r ) increases from 0.044 to 0.297 with the addition of ZnCl2 in the polymerizing system, i.e., [ZnCl2] / [NVP -p MMA] from 0.0 to 0.1. However, the value of r2 (for MMA) decreases from 1.866 to 0.858 at the same concentration of ZnCl2. This indicates that, the reactivity of NVP increases totvards the copolymerization reaction, thus affecting the properties and uses of the obtained copolymers.