Cost-effective pretreatments are essential to overcome the recalcitrant properties of lignocellulosic biomass in order to reutilize cellulosic components within the biomass for value-added products. In this study, a sequential pretreatment of low concentration (< 1.00 vol%) alkaline hydrogen peroxide (AHP) at ambient temperature (~ 25 °C) and pressure (1 atm.) with Type III deep eutectic solvent (DES) was used to fractionate oil palm fronds (OPF). A combination of AHP (0.25 vol%, 90 min) and DES (120 °C, 4 h) at the later stage resulted in a pretreated OPF with a delignification of 18.99%, remarkably improved DES-alone delignification extent by 1.6 folds. The characterizations of pretreated OPF confirmed that mild conditions AHP + DES pretreatment could synergically improve the delignification efficiency. Thus, the use of this sequential pretreatment enabled the lignin extraction and effectively disrupted the recalcitrant structure of OPF, yielding a potential feedstock for a biorefinery process at the later stage.