This research deals with the combination of wood and polylactic acid (PLA), both of which are environmentally friendly materials issued from natural resources and quite easily recycled and degraded in good environmental conditions. Grafting of lactic acid oligomers and polymers onto wood and polymerization into the wood structure have been studied, considering that lactic acid contains carboxylic end groups, while solid wood cell walls contain hydroxyl groups. The main goal of this work was to increase dimensional stability. Weight percent gain (WPG) of beech and Scots pine samples showed 55–60% and 95–105% respectively. As a result, density increased 15–25% in beech and 35–45% in Scots pine. Equilibrium moisture content (EMC) decreased by a similar extent (45–55%) in both wood species, depending on the curing temperature. Higher curing temperature resulted in lower EMC. As a result of lower moisture uptake, anti-swelling-efficiency (ASE) decreased remarkably as well (60–80%). Surface hardness increased as a result of the treatments by 15–40% in cross section and 20–60% in tangential section, depending on wood species. Scanning electron microscopy (SEM) imaging showed that the impregnation was incomplete, as not all cell lumens were filled by the polylactic acid.