Despite of the fact that copper-ethanolamine based solutions have been used for wood preservation for almost 2 decades, the complete mechanism of Cu-ethanolamine fixation is not completely understood. To elucidate interactions between copper-ethanolamine aqueous solutions and wood, Norway spruce (Picea abies) sawdust was immersed to 19 different copper based formulations. These solutions besides copper(II) sulphate contained ethanolamine and quaternary ammonium compoud, sodium borate and/or octanoic acid. pH value of this mixtures was monitored for 4 hours. Immersed sawdust was put to filter paper and washed with one litre of distilled water. Leached impregnated wood was than oven dried (103 °C), and kept in dark and dry place until copper and nitrogen content were determined and correlated to pH changes of sawdust-preservative suspension during impregnation. The result showed that presence of ethanolamine made fixation of copper in wood more effective. Copper absorption to sawdust was affected by concentration of copper, pH value of preservative solution, and it is in tight correlation with pH decrease during impregnation. Furthermore, it was proved that copper and nitrogen absorption into Norway spruce wood were connected as well. Understanding of this mechanism will enable experts to develop preservatives with better performance against weathering and wood pests.