An efficient, nontoxic, and solvent-free oxyalkylation of European beech wood organosolv lignin (OL) has been developed. Two approaches were studied: a direct reaction of lignin with propylene carbonate (PC) and a two-step reaction of lignin with maleic anhydride (MA) followed by oxyalkylation with PC. The structural analysis of lignin polyols was performed by H-1 NMR, C-13 NMR, P-31 NMR, and FTIR spectroscopy. It was demonstrated that PC was able to almost completely oxypropylate aliphatic and phenolic OH groups. Moreover, the carboxylic acid groups of maleated OL were fully oxypropylated by PC. This modification strongly facilitates the generation of a uniform lignin polyol applicable as a biobased component in polyurethanes and polyesters based on cyclic organic carbonates.