The sources of tap water have recently become polluted with a number of chemicals discharged from various industries. Among them, pesticides from golf links and agricultural areas can be considered as priority chemicals for water quality management. In water treatment processes, activated carbon is generally used to remove pollutants. However, humic substances also contaminate environmental water, such as river water. In this study, we examined adsorption isotherms and rates on activated carbon at various temperatures, in order to examine the basic characteristics of adsorption using activated carbon for removal of 2,4-dichlorophenoxy acetic acid (2,4-D), humic substances, and their combination. The adsorption isotherms were correlated with Freundlich-type equation in the concentration ranges tested. Surface diffusion was considered to be dominant. For the selective adsorption treatment for 2,4-D in solotion with humic substances, activated carbon with small pores was more effective than that with large pores.