The importance of fast growing wood species such as Paulownia and Populus wood is increasing. Unfortunately, these wood species do not have durable wood, so they have to be protected for use in outdoor applications. One of the most important groups of wood preservatives for heavy duty applications is the copper based one. Paulownia and Populus wood samples were thus treated with copper-ethanolamine (Cu/MEA) and acid copper chromate (ACC) according to various treatment processes: Bethell, Rüping and dipping. The dipping treatment was performed with various submersion times, ranging from 1 min to 10 days. The uptake of preservative solution, penetration and colour of the specimens were then determined. The results clearly indicate that the permeability of Paulownia is not as good as that of Populus wood. The permeability of Paulownia can be improved with the proper selection of impregnation procedure and wood preservatives. Cu/MEA was found to be more suitable for treatment of Paulownia wood than classical ACC.