A composition for preservation of wood or wood-based materials comprising 1-[[2-(2,4-dichlorophenyl)-1,3-dioxolan-2-yl]methyl]-1H-1,2,4-triazole, at least one of o,o-diethyl o-(3,5,6-trichloro-2-pyridyl) thiophosphate, o,o-diethyl o-(.alpha.-cyanobenzylidene-amino) thiophosphate, O-ethyl o-(2,4-dichlorophenyl)-S-n-propyl dithiophosphate and o,o-diethyl o-(1,6-dihydro-6-oxo-1-phenyl-3-pyridazinyl) thiophosphate, and a suspending agent comprised of at least one of a diluent, an emulsifier and a wetting agent, is provided, together with a process of preparing the composition by mixing the components thereof.