Novel hydroxyl-terminated ionic liquids of 1-(6-hydroxyhexyl)-3-butyl imidazolium bis(trifluoromethyl) sulfonylimide (HHBIM-NTf2) and 1-(8-hydroxyoctyl) -3-butyl imidazolium bis(trifluoromethyl) sulfonylimide (HOBIM-NTf2) were synthesized as stationary phases for capillary gas chromatography (GC). Besides, 1-octyl-3-butyl imidazolium bis(trifluoromethyl) sulfonylimide (OBIM-NTf2) was used as the reference. Selectivities and thermal stabilities of HHBIM-NTf2, HOBIM-NTf2 and OBIM-NTf2 were evaluated by means of the separation of Grob test mixture and positional isomers after the columns were conditioned up to 160 degrees C, 250 degrees C and 300 degrees C, respectively. As a result, baseline separations of Grob test mixture and alcohol mixture and better peak shapes were observed with HHBIM-NTf2 and HOBIM-NTf2. Importantly, baseline separation of dimethoxybenzene isomers was also achieved with HHBIM-NTf2 and HOBIM-NTf2. Satisfactory selectivity of HHBIM-NTf2 still remained even after conditioned at 300 degrees C for 8 h. The results for thermal stability showed that as GC stationary phases, HHBIM-NTf2 and HOBIM-NTf2 were stable at least up to 300 degrees C and 250 degrees C, respectively. The hydroxyl-terminated monocationic ionic liquids possess excellent selectivity and thermal stability and are alternative candidates for GC stationary phases.