The present study investigated the effect of thermal ageing of several wood varnishes on film characteristics. For this purpose, alkyd, two-part polyurethane (urethane-alkyd), and water-borne (self-cross-linked polyurethane) varnishes were applied on Scots pine (Pinus sylvestris L.), Eastern beech (Fagus orientalis L.), and sessile oak (Quercus petraea L.). The test samples had 8% or 12% moisture content. The samples were then thermally aged for 25, 50, 75, and 100 days at 25, 50, 75, and 100 degrees C. The decrease in adhesion strength of the varnish layers and the loss in surface gloss were determined in accordance with the ISO 4624 and ISO 2813 standards. The results of the study indicated that thermal ageing caused a decrease in the adhesion strength and gloss values.