The resistance of subfossil heartwood of European oak (Quercus robur L.) was examined in experiments conducted in accordance with the ASTM D 3345-08: 2009standard. The subfossil heartwood came from Dołhobrody (5100 +/-50 BC) and Pułtusk (13th–14th century). Subfossil heartwood of Q. robur is more susceptible to deterioration by subterranean termites than the recent heartwood of this species. The average weight losses of subfossil heartwood of oak were 0.306 g (Dołhobrody) and 0.475 g (Pułtusk). The average degree of damage to the subfossil heartwood was at the level of moderate attack, penetration. The differences in the degree of damage and weight losses of wood blocks for subfossil heartwood from Dołhobrody and Pułtusk were statistically insignificant. Termite mortality was slight grade (Pułtusk) or slight/moderate grade (Dołhobrody).