This work systematically assessed three acid- or alkali-catalyzed glycerol (AGO/ALGO) pretreatments for lignocellulose fractionation into fermentable sugars and high-quality lignin. Results showed that compared with stand-alone process, catalyst-added pretreatments were more effective in delignification. AGO process had much higher hemicellulose removal selectivity than ALGO, resulting in a 32.7 % lower total sugar content in AGO solids compared to ALGO solids. It was also found that glyceryl lignin could increase cellulose hydrolysis yield, and ALGO lignin showed the highest improvement (35.9 %), which was beneficial to simplify the biorefinery route in the future. NMR analysis revealed that ALGO pretreatment was more favorable for lignin hydroxylation grafting reaction than AGO process, making recovered lignin have more β-O-4 linkages and aliphatic -OH groups. These results present pivotal insight into the design of organosolv pretreatment, aiming at platform sugar and lignin coproducts.