Abstract: The GCseparation properties of the mixed stationary phase of two cyclodextrin derivatives(permethy1-β-cyclodextrin and heptakis(2,6-di-O-pentyl-3-O-allyl)-β-cyclodextrin) werestudied using benzene positional isomers. The separation mechanism on mixed stationaryphase was discussed from column efficiency, structure of stationary phase and theinteraction mode between stationary phases and solute. Most of positional isomers ofdisubstituted benzene were well separated on the mixed stationary phase column, with theseparation of bromotoluene, nitrotoluene etc. on the mixed stationary phase columndemonstrating synergistic effects. The GC properties of the mixed stationary phase of twocyclodextrin derivatives are different from that of the conventional mixed stationaryphases.