Natural durability of solid wood of Italian poplars is very low. Samples of 4 species-Populcs deltoides cv. "Harvard" (ex. 1-63/51). Populus euramericana cv. "San Martina" (ex. 1-72/58), Fraxinus mandshurica Rupr. and Tilia amanurensis Rupr. were subjected to wooddestroying fungus (Lenzites Irabea Pers. ex Fr.) for one andhalf months in the soil block test. In decay test, although the mean percent of weight loss of plywood and oriented flakeboard of poplars was slightly lower than wood, they were still perishable. They may be molded very easily. Therefore it is important to improve the durability of wood and wood products in the utilization of poplars.Composite boards of Italian poplars were treated with chromated zinc chloride (CZC). The effect of treatment was evident. The weight loss of poplars plywood and oriented flakeboard treated by impregnation with a 1.5g/l solution of the preservative for an hour and a half was lower than those of ash and bass wood. Dry salt retention of wood is about 6.5kg/m3 after treatment with a 3.0g/l solution, and 9.2kg/m3 with 4.5g/l solution. The former can be used in a severe fungus and/or insect attack condition and the latter even in more serious conditions.After impregnating for one and half hours, the moisture content of plywood was 42-45 percent, and oriented flakeboard 21-26 percent. The weight concentration of CZC is the main factor which determines the salt retention of treated wood, whereas the absorptivity and moisture content of wood are of minor importance.