Abstract: The present invention provides a wood preservative composition and a process for treating wood with the composition for protecting wood from decay and insect attack. The invention further provides a wood preservative composition comprising dispersed particles of a copper compound and a polydentate ligand. The composition can be used to treat difficult-to-treat wood species including hem fir, Douglas-fir, ponderosa pine, red pine, redwood, cedar, and spruce to achieve effective copper penetration.