Abstract: The adsorption properties of mercury ions onto a novel copolyaniline, which is modified by m-aminobenzenesulfonic acid via chemically oxidative polymerization, were studied in a batch system. It was found that the copolyaniline has shown an excellent absorbability for mercury ions. The removal efficiency of mercury ions from the wastewater was above 98.4% when mercury ion concentration was less than 750 mgL-1. When mercury-ion concentration of wastewater was 1 980 mgL-1, the adsorption capacity of 20 mg copolyaniline could reach as high as 1 113.6 mgg-1. When mercury-ion concentration of wastewater was as low as 20 mgL-1, a very high removal efficiency of 99.99% could be achieved. After treatment the residual mercury-ion solution can meet the national wastewater-discharging standard.