The factors affecting thermostability and reactivation of peroxidase from soybean sprouts(Glycine max L.) were investigated. The enzyme was the most stable at pH 7.0 and below 60oC. Thermostability of the enzyme was reduced by addition of sodium chloride and saccharides. The partially inactivated enzyme by heat treatment at 75oC for 10 min was reactivated up to 211.5% at the optimal reactivation condition. The optimal pH and temperature for reactivation of the enzyme were pH 9.0 and 40oC, respectively. The reactivation was completely inhibited by addition of sulfhydryl reagent such as L cysteine.