Scots pine and white poplar were modified with melamine formaldehyde (MF) and melamine-urea formaldehyde (MUF) resins to improve their physical and mechanical properties. Impregnation was conducted at 4 bar pressure for 30 or 60 min, and the samples were cured at a temperature of 150 °C for 40 min in an oven. The density, equilibrium moisture content, weight percent gain, bulking effect, water uptake, volumetric swelling, anti-swelling efficiency, modulus of rupture, modulus of elasticity, compression strength parallel to the grain, and Brinell hardness of the modified wood were determined. The anti-swelling efficiencies were 57% and 74% in Scots pine and white poplar, respectively, using the melamine formaldehyde resin. Modification of white poplar with melamine-urea formaldehyde increased the modulus of elasticity, compression strength, and Brinell hardness considerably. Both resins were successful at improving the physical and mechanical properties of Scots pine and white poplar woods.