The styrene-maleic anhydride copolymer (SMA) was modified by alcohol. The effect of modified-conditions, such as reaction time and temperature, amounts of catalyst, amounts of alcohol on degree of esterification was further investigated. FTIR results showed that the anhydride in SMA successfully reacted with alcohols. The degree of esterification reached to 35% when molar ratio of isobutanol to SMA was about 12%, the mass ratio of p-toluenesulfonate was about 1%, and the reaction temperature was 80oC for 4 hours. The modified-SMA (SME) showed an excellent dispersing ability for carbon black. The ultrafine carbon black dispersion with 160nm would be obtained when degree of esterification was higher than 15%, the mass ratio of SME to carbon black was about 20%, and pH value was 9. The prepared carbon black dispersion with SME showed an improved stability to temperature and centrifugal forces.