The effect of trehalose on the refolding of denatured lysozyme was investigated at different guanidine hydrochloride（GdnHCl）concentrations.The competitive model of first-order folding and third-order aggregation could well describe the dynamic refolding process in the presence of trehalose.It was found that aggregation rate constant kA decreased obviously by adding trehalose，but the folding rate constant kN was little affected.At a proper concentration of GdnHCl，kA decreased first and then increased with increasing trehalose concentration.At the optimal trehalose concentration，the aggregation rate constant kA reached a minimum，while the ratio of kN/kA reached a maximum correspondingly.Thus，at this additive concentration a maximum refolding yield was obtained.The result indicated that the main role of trehalose was to prevent intermolecular aggregation.Therefore，in a proper range of concentration，increasing trehalose concentration could facilitate refolding of protein and increase refolding yield.