Poly(2,5-benzimidazole) membrane (ABPBI) was investigated for the removal of phosphate species from aqueous solution. This work was conducted to provide fundamental information from the study of equilibrium adsorption isotherms, and to investigate the adsorption mechanisms in the removal of phosphate species using ABPBI. Batch experiments were performed under various conditions of initial phosphate concentration, pH, and contact time. The Langmuir monolayer adsorption capacity of ABPBI was calculated as 87.90 mg/g. The pseudo-first-order kinetic, pseudo-second-order kinetic, and the intra-particle diffusion models were used to describe the kinetic data and rate constants were evaluated. The activation energy for degradation estimated by Kissinger method for ABPBI was found to be 62.6 kJ/mol in air atmosphere. The physicochemical properties of ABPBI were investigated by FT-IR, TGA, and SEM techniques.