AbstractIn this experiment, Acacia mangium wood was physically activated in the presence of CO2 gas at an activation temperature of 500 ºC for 2 h. The total surface area of the activated carbon was found to be 395.91 m2/g, 81.06% of which was due to micropores. Fourier transform infrared spectroscopy showed that the major functional groups on the surface of activated carbon were carboxylate, hydroxyl, and lactone groups. An isotherm study of methyl orange dye adsorption by the activated carbons was conducted. Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich (D-R) isotherms were applied to find the adsorption characteristics of the activated carbon. The results showed that the isotherm data followed the Langmuir isotherm with maximum adsorption capacity of 7.54 mg/g at a temperature of 25 °C and an equilibrium time of 48 h. A dimensionless equilibrium constant, RL equal to 0.3280 was also determined to prove that adsorption was favorable but not very effective.