The fabrication of molecular sieves and carbon-based adsorbents by pyrolysis of lignocellulosic material, such as Salix viminalis wood, generates a considerable amount of pyrolysis oil which has no specific application. In the present paper, we investigate phenolic components of S. viminalis derived pyrolysis oil with regard to their potential application to the oxidative stabilization of synthetic lubricating oils. Two phenolic fractions were isolated through solvent extraction (extract A was ether soluble; extract B was methylene chloride soluble) and characterized by chromatographic analysis. High levels of 2,6-dimethoxyphenol and its para-substituted derivatives were attributed to a rather atypical composition of S. viminalis lignin. The antioxidative effect of pyrolysis-derived polyphenols on diesters and their blends with poly-alpha-olefins was studied by means of a high temperature oxidation test combined with spectroscopic (NMR and FT-IR) product analysis. The test proved that the antioxidant capacity of each extract is high, at the level of ca. 1000 ppm. Extract A had the highest increase in the induction period (170 h), and compared with the commercial BHT antioxidant, it prolonged the lag phase ca. 3.3 times. The effect of the o-methoxy and para substituents, intramolecular hydrogen bonding of the hydroxyl H atom, and synergetic interactions on the antioxidant activity is discussed.