Various natural products are potentially suitable for wood protection, particularly against fungi attack. Caffeine is a well-known compound of natural origin, commercially and economically available, which could facilitate its future use for wood protection. This work investigated the antifungal resistance of the sapwood of Scots pine (Pinus sylvestris L.) treated with a water solution of caffeine and then thermally modified. The samples after impregnation were thermally modified at different temperatures selected on the basis of thermogravimetric analysis (TGA) of caffeine. The paper presents preliminary results of resistance of treated pinewood towards Aspergillus niger van Tieghem (ATCC 6275). The treated samples were subjected to both a leaching procedure and to the artificial aging procedure imitating natural weather conditions. Thermal modification of wood treated with caffeine improved the fungistatic properties of samples after artificial aging. It occurred through partial elimination of caffeine leaching from the wood structure.