Pretreatment is an essential step for the bio-refinery to degrade the recalcitrance of lignocellulosic biomass structure, thus facilitating the accessibility of cellulose-degrading enzymes. In this study, pretreatment of oil palm empty fruit bunch (OPEFB) by the dilute acid (maleic and sulfuric acid) solution under microwave irradiation was investigated. The pretreatment was conducted at 160, 180, and 200 °C for 10 min, and at 180 °C for 5, 10, and 15 min. The pulp recovery, reducing sugars, and glucose released after enzymatic saccharification of pretreated OPEFB were determined. Lower pulp recovery was achieved at the higher pretreatment temperature by sulfuric and maleic acids. The reducing sugars released after enzymatic saccharification of OPEFB pretreated by maleic acid for 10 min at 160, 180, and 200 °C were 31.4, 38.7, and 40.4 g/100 g initial biomass, respectively. This result indicating the deformation of OPEFB structure by maleic acid at higher temperature successfully facilitates the enzyme to access and degrade cellulose in the pulp. However, in the case of sulfuric acid pretreatment, reducing sugars released was dropping at high temperatures. The cellulose conversion into glucose by enzymatic scarification of pretreated OPEFB was higher compared to that of untreated OPEFB. Pretreatment at 180 °C for 10 min by sulfuric and maleic acids resulted in 84.0 and 86.5% cellulose conversion, respectively. These values are about 4 times higher than the cellulose conversion from untreated OPEFB (21.8%).