Effects of residual-lignin structure-expressed as the syringaldehyde to vanillin (S/V) ratio-on the enzymatic saccharification rate was studied as a key step of bio-ethanol production. Alkaline sulfite-anthraquinone (AS-AQ) and soda-AQ cooking methods were applied to delignification of sugarcane bagasse (SB) and oil palm trunk (OPT) , and the resulting pulp samples were subjected to enzymatic saccharification. The S/V ratios of residual lignin in the pulp were determined by the nitrobenzene oxidation method. This study