The objective of this work is to develop a green method forthe speciation of mercury compounds by coupling IC to ICP-MS (IC-ICP-MS) using an aqueous mobile phase that contains low concentrations of reagents. We here report on the development of a hyphenated method for mercury speciation by cationexchange chromatography with ICP-MS detection. Using l-cysteine(or thiourea) as the complexing agent in the aqueous mobile phase,baseline separation of four mercury species (Hg2+, MeHg, EtHg andPhHg) was achieved in 2.5 min by using two consecutive 12.5-mm strong cation exchange (SCX) guard columns. Key factors of the mobile phase such as pH, flow rate and complexing reagentconcentration were further investigated. To validate this method,the analysis of certified reference materials of seawater (GBW(E)080042) and fish tissue (GBW 10029) was conducted and therecovery of the mercury species was also performed. Finally, theproposed method was applied to the mercury speciation in fiveseawater samples and five marine fish samples.