Durability of wood depends on natural durability, design, and applied chemical preservation. One of the most important biocides used in commercial wood preservatives are copper compounds. Recent experiences showed that despite of the widely used copper compounds their efficacy was not sufficient. The purpose of this work is to elucidate, if the pH of the wood improves fungicidal properties of the copper treated wood. The experiment was performed on spruce softwood specimens, exposed to wood decay fungi according to the mini block procedure. In the experiment the following fungi were utilised: Antrodia vaillantii, Gloeophyllum trabeum, Hypoxylon fragiforme, Serpula lacrymans. Specimens were vacuum impregnated with 2 different copper based solutions (CC and CuE) of 2 different concentrations (cCu = 0.1 % and cCu = 0.25 %). Impregnated specimens were afterwards soaked with 3 aqueous buffer solutions: pH 5, pH 7, pH 9 and H2O. The results show that higher (basic) pH values significantly increase efficacy of the copper based preservatives against copper tolerant fungi Antrodia vaillantii. Basic pH values are not favoured by Hypoxylon fragiforme and Serpula lacrymans, as well. In contrary, wood decay fungus Gloeophyllum trabeum decays considerably more alkaline copper treated wood compared to copper treated wood soaked with water only.