The adsorption characteristics of metsulfuron-methyl (MM) onto powdered activated carbon (PAC) and granular activated carbon (GAC) were studied at varying solution pHs (4-9) and temperatures (20-40 degrees C). The dependence of pH was observed in aqueous solution with MM. The film mass transfer and intraparticle diffusion coefficients were estimated from concentration decay curves obtained in the batch adsorber. The maximum adsorption capacity decreased with increasing pH and temperature. Among the PAC used, the coconut based PAC had the best adsorption capacity. The adsorption isotherms could be plotted using the Freundlich and Toth models with a reasonable degree of accuracy. The overall adsorption isotherm such as the modified-Toth model should be applied. The performances of the fixed- bed GAC system was also simulated by a model developed. The objective of the present study was to investigate the adsorption and pH dependence behavior of MM onto PAC and GAC in order to diminish the environmental risk of MM pollution.