AbstractThe effects of acid copper chromate (ACC) and hydrothermal treatments were determined relative to the hardness, decay resistance, and dimensional stability of poplar wood. Test specimens, prepared from poplar wood (Populus nigra L.), were first heat-treated under saturated steam in a digester and then impregnated with ACC solution and by a long-term (21 days) dipping technique to reach complete saturation. Impregnated specimens were exposed to white-rot fungus (Trametes versicolor) for 14 weeks, using the Kolle flask method. The weight loss and Brinell hardness were determined after impregnation, thermal treatment, and exposure to T. versicolor. The combination of thermal treatment and ACC preservative on the poplar wood showed improved hardness and decay resistance properties of wood, depending on the treatment time and temperature. The highest weight loss (37.78%) was observed for control specimens, and the lowest (3.03%) occurred in 1% ACC-treated specimens. The highest Brinell hardness on a tangential surface was observed in 1% ACC-treated specimens (6.45 kN), and the lowest was noted in the specimens heat-treated at 130 °C and 180 min (0.52 kN).