AbstractOxidative polymerization of two isolated lignans, secoisolariciresinol, and secoisolariciresinol diglucoside, as well as the lignan macromolecule, by a high redox potential Trametes hirsuta laccase was studied with different analytical methods. The reactivity of laccase with the different compounds was studied by an oxygen consumption measurement. The polymerization of laccase-treated lignans was evidenced by size exclusion chromatography, reversed phase - high performance liquid chromatography, and matrix-assisted laser desorption/ionisation - time of flight mass spectrometry. The data showed that the selected substrates could be oxidised by laccase. Secoisolariciresinol and secoisolariciresinol diglucoside were polymerized by laccase to a similar extent. The lignan macromolecule reacted to a lesser extent. Polymerization of the macromolecule proceeded mainly via its secoisolariciresinol diglucoside moieties. Furthermore, it was shown that ferulic acid can be linked to polymerized secoisolariciresinol via decarboxylation by laccase. This investigation showed that lignans can be enzymatically modified by Trametes hirsuta laccase.