The adsorption of sulfonamides by carbon black from solution was investigated in detail regarding the hydrophobic interaction. The adsorption isotherms obtained were well described with Langmuir equation. pH and concentration of buffer solution had no distinct effect on the adsorption of sulfonamides near the neutral pH region. From the following results, it was convinced that the adsorption of sulfonamides by carbon black from aqueous solution proceeds by the hydrophobic interaction : (1) adsorption of sulfonamides by carbon black from MeOH solution was correlated to that from aqueous solution ; (2) adsorption of sulfonamides by graphite from aqueous solution was correlated to that by carbon black ; (3) the entropy change of adsorption of sulfonamides by carbon black from aqueous solution was positive.