Kraft lignin (KL) was successfully depolymerized into polyols of moderately high hydroxyl number and yield with moderately low weight-average molecular weight (M-w) via direct hydrolysis using NaOH as a catalyst, without any organic solvent/capping agent. The effects of process parameters including reaction temperature, reaction time, NaOH/lignin ratio (w/w) and substrate concentration were investigated and the polyols/depolymerized lignins (DLs) obtained were characterized with GPC-UV, FTIR-ATR, H-1 NMR, Elemental & TOC analyzer. The best operating conditions appeared to be at 250 degrees C, 1 h, and NaOH/lignin ratio approximate to 0.28 with 20 wt.% substrate concentration, leading to <0.5% solid residues and similar to 92% yield of DL (aliphatic-hydroxyl number approximate to 352 mg KOH/mg and M-w approximate to 3310 g/mole), suitable for replacement of polyols in polyurethane foam synthesis. The overall % carbon recovery under the above best conditions was similar to 90%. A higher temperature favored reduced M-w of the polyols while a longer reaction time promoted dehydration/condensation reactions. (C) 2013 Elsevier Ltd. All rights reserved.