The applicability of eco-friendly corrosion inhibitors to control metals degradation in aggressive media has been considered in recent years.Our previous research showed that marine Vibrio neocaledonicus sp.bacterium and its exopolysaccharide have the high corrosion inhibitory effect for carbon steel in artificial seawater.In this work, the corrosion inhibitory effect of microbial exopolysaccharide for carbon steel in 0.5 M H2SO4 solution was investigated.Weight loss, electrochemical measurements and FESEM were applied to study the mechanism and corrosion inhibitory efficiency.It is found that this compound is an efficient corrosion inhibitor in 0.5 M H2SO4 solution and the highest inhibition efficiency observed at optimum concentration (1000 ppm).The synergism effect of halides was also studied and results showed that inhibition efficiency increased significantly with addition of halides follow the trend of Cl-< Br-< I-.Inhibitor alone and in combination with halides obeys Langmuir adsorption isotherm.Phenomenon of chemical adsorption is proposed from the trend of inhibition efficiency with the values AG0ads.