This　study　explored　diethanolammonium　chloride　([DEA]Cl)　as　a　potential　ionic　liquid　from　low-cost　and　commercial　ones　for　gas　separation.　There　are　three　kinds　of　functional　sites　in　[DEA]Cl:　acidic　-NH2+,　hydrogen-bond　-OH,　and　nucleophilic　Cl−.　The　separation　of　NH3/N2/H2,　SO2/CO2/N2,　and　H2S/CO2/CH4　was　considered,　because　the　three　mixtures　are　extensively　involved　in　many　industrial　processes.　The　experimental　results　demonstrated　that　[DEA]Cl　exhibited　excellent　ability　to　separate　the　mixture　of　NH3/N2/H2.　The　[DEA]Cl　also　exhibited　the　proper　capacity　to　separate　SO2/CO2/N2,　but　the　capacity　of　[DEA]Cl　for　the　separation　of　H2S/CO2/CH4　was　inferior.　The　theoretical　calculations　revealed　that　-NH2+　and　-OH　worked　synergistically　to　contribute　to　the　ability　of　[DEA]Cl　for　excellent　separation　of　NH3　from　NH3/N2/H2,　with　Cl−　contributing　to　the　proper　separation　of　SO2　from　SO2/CO2/N2.　This　study　provides　experimental　and　theoretical　basis　for　the　industrial　application　of　[DEA]Cl　in　the　area　of　gas　separation.　©　2023　American　Institute　of　Chemical　Engineers.