Abstract: The adsorption of Congo Red (CR) onto Bottom Ash (BA) was studied in batch process. The objective of this study was to compare the adsorption capacity between physical-activated BA and untreated BA for removal of CR. Bottom ash was modified by undergoing pyrolysis process where it was activated in the vertical tubular furnace with the flowing of carbon dioxide at 700°C. Then, the adsorption process was carried out on an orbital shaker at 150 rpm for 24 h. Adsorption equilibrium of CR was attained after 24 h of contact time. The equilibrium adsorption data were interpreted by using Langmuir and Freundlich models. The data shows that physical-activated BA and untreated BA were well described by the Freundlich model. In addition, the amount of CR adsorbed on the adsorbent, qe was higher using physical-activated BA (106.61 mg g-1) as compared to untreated BA (24.36 mg g-1). In conclusion, the modification of BA using pyrolysis process offered a significant affects to the performance of the BA for removal of CR.