From the renaturation kinetics of denatured/reduced lysozyme assisted by the molecular chaperone GroEL, a simplified kinetic model was established based on the competition between protein folding and aggregation. In the presence of GroEL and ATP, the aggregate formation was a second order reaction. With 2 mM ATP, a renaturation yield of 90% at a high renaturation rate was obtained when the molar ratio of GroEL to lysozyme was 1:1.