Activated carbon was prepared using bituminous coal by steam activation process in a laboratory scale rotary type furnace. The physical properties and porosity of the chars were investigated. The optimum conditions of manufacturing process of activated carbon were suggested by observing the development of pores during the activation process. Generally, the adsorption capacity of activated carbon decreased with increasing the activated carbon yield (AC yield). However, the adsorption capacity and the pore characteristics such as BET surface area or pore volume etc., showed a similar tendency. It was found that the maximum adsorption capacity and pore development were obtained from the activation process showing about 35∼40% AC yield, which was strongly affected by raw materials and activation condition.