Abstract1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) was used to enhance the dimensional stability, fungal resistance, and weathering of wood. The mechanical strength of wood treated with DMDHEU and different catalysts at different treating temperatures was studied. With increasing temperature, the modulus of rupture (MOR) and modulus of elasticity (MOE) of DMDHEU-treated wood first increased and then decreased. Different catalysts exhibited different effects on the MOR and MOE. In the context of SEM, EDAX, and FTIR analyses, the mechanism of strength loss resulting from the treatment with DMDHEU is discussed. In addition, the relationship between strength and pore size distribution determined by DSC was studied. The filling effect of the cured DMDHEU in wood pores reduced the pore size of the samples and may provide mechanical support to the cell wall, which prevents strength loss of the treated wood when the curing temperature is relatively low (90˚C). But at higher curing temperatures (150˚C), the mechanical strength properties of DMDHEU-treated wood decreased greatly.