In this study, fir (Abies nordmanniana) and poplar (Populus sp.) woods were modified with citric acid and five different polyols (glucose, sorbitol, glycerol, sucrose, and maltodextrin) at 10% concentration for 2 hours at 150℃. Equilibrium moisture content, water uptake, anti-swelling efficiency, compression strength parallel to the grain, anti-bacterial test, and decay test were applied to measure the changes in the modified wood. As a result, the equilibrium moisture content at 90% RH and the water uptake rates of the modified woods decreased, but the anti-swelling efficiency increased up to 57%. Compression strength parallel to the grain increased by 10% in fir wood and 21.3% in poplar wood. Anti-bacterial properties were observed withcitric acid in fir wood and citric acid, citric acid/sorbitol, citric acid/glycerol samples in poplar wood. As a result of the fungal decay test, the weight loss of the wood samples was between 4.46 and 7.65% in fir wood and between 6.51 and 12.70% in poplar wood. The modification conditions of wood samples were optimized with citric acid, which improved wood properties by blocking reactive groups by cross-linking on wood fibers. As a result, citric acid treatment improved some physical, mechanical, and biological properties of fir and poplar wood, and it is recommended as a promising, environmentally friendly, and cost-effective wood preservation method.