Southern pine (Pinus spp.) wood cubes were treated with amine copper quaternary (ACQ) solutions supplemented with wax and different types of nano-SiO2 particles. The effects of various types of nano-SiO2 on the dimensional stability of ACQ-treated wood were investigated, including water absorption, swelling, and shrinkage. The results showed that nano-SiO2/wax treatments improved the hydrophobicity of the ACQ-treated wood; various types of nano-SiO2 particles had different effects on the water absorption by the wood. The best water absorption resistance was observed with the ACQ-treated wood modified with nano-SiO2 that had a specific surface area of 380 m2/g. However, the nano-SiO2/wax treatment had a negligible effect on the swelling and shrinkage resistance of the ACQ-treated wood; various types of nano-SiO2 did not affect the swelling and shrinkage of the wood.