The curing reaction of two kinds of UF resins has been studied, namely, for plywood （F/U=1.7） and for particleboard （F/U=1.63）, in the presence of NH,4,Cl hardener The result shows that there is a clear exothermic peak below 100℃ with NH,4,Cl. The temperature of the. peak （Tp） hardly changes at a definite time range, bout the exothermic heat （ΔH） and the height of the peak lower with time The Tplowers and the height of the peak rises with increase of NH,4,Cl amount, when the amount is about 1.5%（based dry resin）both of them are no change.The exothermic peak is concerned with the disappearance of the group-CH,2,OH, and then a primary curing reaction of UF resin takes place. The curing reaction order is 1.5, the active energy is 80 KJ/mol with 1.7% NH,4,Cl （based dry resin） according to kissinger’s method by DSC.