Oil palm EFB fibers were used to remove cationic MB and anionic PR from aqueous solutions. The adsorption of PR on the PEI-EFB fibers achieved faster equilibrium than the adsorption of MB on the CA-EFB, which may have been due to its higher surface charge. The experimental data of the adsorption of MB onto CA-EFB fitted the Langmuir isotherm while the adsorption of PR onto PEI-EFB fitted Freundlich isotherm, suggesting the distinct adsorption behavior of dyes onto both adsorbents. The regeneration studies proved that both CA-EFB and PEI-EFB can be reused for more than seven cycles of adsorption/desorption with not more than 30% of adsorption capacity loss. Therefore, the feasibility of the adsorbents for large scale adsorption, such as fixed-bed, is worth to be investigated.