Indonesia is predicted to create 11.11 million metric tons of oil palm empty fruit bunches (OPEFB) each year as a waste. Because of the high cellulose content, this waste has the potential to be processed into a valuable product such as bioethanol. In this study, liquid hot water-assisted dilute sulphuric acid (LHW-SA) for 67.17 min at 180 °C was used as a pretreatment method to breakdown the matrix structure of OPEFB, and eventually cellulose could be converted into reducing sugar. Both filtrate and residue after pretreatment were investigated for chemical and physical properties. Analysis of liquid fraction showed that LHW-SA generates reducing sugar and a brown compound which may correlate with cellulose and hemicellulose degradation. The degradations were also shown in the chemical composition analysis of the residue as well as in functional group alteration of FTIR spectra. In the pretreated pulp, peak intensity corresponded to C–H bending of the methoxyl group at 1371 cm−1 was diminished. Besides, the crystallinity index analysed by XRD showed a decreasing amorphous component. LHW-SA also caused a rupture in the morphological structure of OPEFB that was attributed to increased enzyme accessibility. After enzymatic hydrolysis, as much as 40% reducing sugar yield was obtained. That proved the effectiveness of LHW-SA pretreatment to increase reducing sugar yield.