Hydrogen sulfide was oxidatively absorbed by iron-containing ionic liquids, which were synthesized in different molar ratios of FeCl3 center dot 6H(2)O to 1-butyl-3-methylimidazolium chloride. It was found 1-butyl-3-methylimidazolium tetrachloroferrate ([bmim]Fe(III)Cl-4), being highly reactive toward H2S, was the dominating iron(III) species independent of molar ratios, but the concentration of iron and chloride as well as the acidic strength lowered with the decrease of molar ratio from 2 to 0.3. Moreover, the acidity and iron(III) concentration had important influence on oxidation of H2S, but their significance varied with the temperature. HCl emissions were also discovered in the oxidation of H2S to S-8 and the reduction of [bmim]Fe(III)Cl-4 to [bmim]Fe(II)Cl4H. A way for controlling HCl emissions was proposed, involving the decrease in the chloride concentration of iron-containing ionic liquids in the presence of water.