Fast-growing poplar wood with better water-resistance property was obtained via a one-step impregnation of maleic rosin (MAR). MAR was prepared by modifying natural rosin acid with maleic anhydride. The wettability, weight percent gain (WPG), density, anti-swelling efficiency (ASE), and mechanical properties of modified wood were investigated in detail. The morphology, chemical composition, and thermal stability of modified wood were characterized. The formation mechanism of poplar wood specimens was elaborately described. Results demonstrated that the wood, after the treatment with 20% MAR solution (20% refers to the percentage of mass of MAR per mass of anhydrous ethanol), was hydrophobic and had a water contact angle (CA) of 142. In addition, the dynamic wettability of wood was significantly changed by MAR treatment. The density of the wood increased by 15% after the treatment with 30% MAR solution. Furthermore, the bending strength (BS) and modulus of elasticity of the wood treated with 30% MAR solution increased to 83.23 GPa and 7.08 MPa, respectively.