Summary Electrospray ionisation Fourier transform ion cyclotron resonance mass spectrometry (MS) and size exclusion chromatography (SEC) was utilised for analysis of milled wood lignin (MWL) and lignin model compounds degraded by thioacidolysis. MS and SEC showed that thioacidolysis was an efficient method for degradation of the β-O-4 bond in lignin. Moreover, the molecular weight of thioacidolysed pinoresinol and MWL were analysed using matrix assisted laser desorption ionisation time-of-flight mass spectrometry. Tandem MS was successfully applied for the structural determination of thioacidolysed pinoresinol with and without acetylation of the product. The MS results of thioacidolysis on MWL resulted in the identification of a tetrameric lignin structure containing a 5-O-4, 5-5, β-1 linkage pattern.