This study investigated, by differential scanning calorimetry, the thermal curing behavior of urea-formaldehyde (UF) resins modified with two formaldehyde scavengers and its impact on the adhesion performance of particleboard bonded with modified UF resin adhesives. As the concentration of the two scavengers [i.e., urea-formaldehyde prepolymer (UFP) and urea solution (US)] increased, the gel time, peak temperature, and onset temperature of the modified UF resins did not change significantly for UFP-modified UF resins, but these parameters increased for the US-modified UF resins. These results indicated that the reactivity of the UF resin modified with UFP was maintained, but it deteriorated for the US-modified UF resins. The formaldehyde emission of particleboard bonded with the modified UF resin decreased with an increase in the scavenger concentration. UFP was more effective than US in scavenging the formaldehyde emission and in achieving adhesion to the UF resin. The results showed an optimum UFP level of 20% in the UF resin for maintaining a balance between the formaldehyde emission and adhesion of the particleboard, and they indicated that both the thermal curing behavior of scavenger-modified UF resins and the properties of particleboard bonded with them must be taken into account in the evaluation of a formaldehyde scavenger system. (C) 2008 Wiley Periodicals, Inc.