The density, swelling, and fungal decay of poplar (Populus deltoides) wood treated with pistachio resin (PR) obtained from Pistacia atlantica were investigated. The white-rot fungus Trametes versicolor and the brown-rot fungus Coniophora puteana were used. Methanolic solutions of PR with different concentrations of 1%, 6%, 12%, and 15% were used as the preservative solution. Wood samples were saturated by two different vacuum/pressure (V/P) and dipping methods. The density, volumetric swelling of treated wood, and their mass loss (ML) caused by fungal decay were determined. The density of treated species increased to 15.4% and 5.8% for V/P and dipping methods, respectively, at 15% PR concentration. The volumetric swelling of the treated samples was reduced to 24.5% and 16.8% for V/P and dipping procedure, respectively, at 15% PR concentration. The mass loss of treated samples after exposure to T. versicolor was less than the untreated one (17.4% for V/P and 22.6% for dipping methods at 15% PR concentration). The results showed the better performance of V/P treatment in promotion of wood durability against fungal decay than the dipping method.