Lignocellulosic biomass is a plant dry matter that could be considered as a renewable carbon resource for the production of reducing sugar, which is an alternative building block for biofuels and chemicals. However, due to the recalcitrant nature of lignocellulosic biomass, researchers have focused their efforts on establishing cost-efficient pretreatments to reutilize the lignocellulose components within the biomass effectively. In this study, divalent (CuCl2) and trivalent (FeC1(3)) inorganic salts were used in the recovery of xylose from the stalks of oil palm fronds (OPF). Additionally, oxidizing agents such as hydrogen peroxide and sodium persulfate were tested for their effectiveness in improving inorganic salt pretreatment. By using inorganic salt alone, FeC13 outperformed CuCl2 in terms of xylose recovery, in which 75.5 and 59.3% of xylose could be recovered from OPF using FeC13 and CuCl2, respectively. An incorporation of sodium persulfate with CuCl2 enabled a maximum xylose recovery up to 72.0%, with no statistical difference as compared to using FeCI3 alone. The synergism between CuCl2 and sodium per sulfate was attributed to the formation of unstable Cu3+ ions, which acted as a trivalent salt. Characterization studies of the solid fraction before and after pretreatment also validated the delignification of OPF. Hence, the combination of CuCl2 and sodium persulfate was able to attain sugar yields which were comparable with other conventional pretreatments. (C) 2017 Elsevier Ltd. All rights reserved.