In this investigation,the surface-ohemical.properties of the mixed aqueous solutions of n-octyltrimethylamnnonium bromide(C₈ NMe₃Br) and sodium n-octylsul-fate(C₈SNa) have been studied.Some peouliar properties have been observed:(1) there is a very high surface aotivity of the mixed surfactants.The cmc of 1:1(molar ratio) mixture is 7.5×10^-3 m(cmc of C₈NMe₃Br:2.6×10^-1).The surface and interfaoial tension of 1:1 mixture are very low-down to -23 and -0.2 dyne/cm,whereas those of the single ionic surfactant solution(at cmc or above) are -40 and -10 dyne/cm,respectively;(2) the bubble-life and the drop-life of 1:1 mixture are both much longer than those of the single surfactant solution.