Ferric (III) chloride, when prepared as an ionic solution, was used to pretreat oil palm empty fruit bunch (OPEFB) before undergoing enzymatic hydrolysis to convert into value-added products. The pretreatment was assisted with microwave irradiation to improve the degradation of recalcitrant structure of lignocellulosic materials with minimum time. The effects of salt concentration, temperature, and duration of pretreatment on the chemical composition of OPEFB and total reducing sugar (TRS) yield were investigated. The results revealed that the best pretreatment occurred at pretreatment time of 10 min, 100 °C, and ferric chloride concentration of 10 w/v%. The TRS yield achieved using the pretreated OPEFB was approximately 0.485 g/g, which was three times higher than the non-pretreated OPEFB, which was only 0.154 g/g. Thus, the ionic solution pretreatment method is a promising alternative for replacing other pretreatment methods.