AbstractThis study was performed to determine the effects of thermal aging on the film hardness of some wood varnishes. For this purpose, Scots pine (Pinus sylvestris L.), Eastern beech (Fagus orientalis L.), and oak (Quercus petraea L.) samples coated with synthetic (alkyd), two-part polyurethane (urethane-alkyd), and waterborne (self cross-linked polyurethane) varnishes were evaluated at a moisture content of 8% and 12%. Afterwards, thermal aging processes were performed for periods of 25, 50, 75, and 100 days at 25 ºC, 50 ºC, 75 ºC, and 100 ºC. Hardness changes in the varnish films were measured in accordance with ISO 1522-2006. According to the test results, the samples prepared with polyurethane varnishes at 8% moisture content give the best results.