The effectiveness of combined mechanical-chemical pre-treatment on oil palm empty fruit bunch (EFB) fibers in removing organic dye from aqueous solution was studied. The efficiency of dye adsorption in aqueous solution using natural fibers is generally affected by several factors, such as pH, temperature, and the concentration of dye. However, the effect of the size of the fibers (adsorbent) has rarely been investigated. Prior to any MB adsorption process, mechanical-chemical pre-treatment was performed on EFB fibers via a high-shear process using a Silverson mixer. Shearing duration and the introduction of sodium hydroxide (NaOH) influenced the rate of adsorption, due to the changes in fiber size and accessible surface after the treatment process. From these results, it was found that smaller EFB fibers enhanced the rate and adsorption capacity of MB. However, this was not a linear relationship, as the rate of adsorption decreased when the shearing duration was prolonged to 30 minutes. Meanwhile, treatment with 0.1 M NaOH also improved the adsorption performance of the fibers. Hence, combined mechanicalchemical pre-treatment of EFB fibers can increase the adsorption rate and capacity of the fibers. This study may provide useful information on a practical pre-treatment approach for natural fibers as dye adsorbent in wastewater treatment.