Abstract: The effect of short chain monohydric alcohols (ethanol, n-butanol) and dihydric alcohols (ethyleneglycol, 1,4-butanediol) on the aqueous two-phase system (ATPS) of cationic and anionic surfactants (SDS-CTAB) is studied. Results show that the additions of monohydric alcohols can not only shorten the phase separation time, expand the regions of ATPS but also cause the formation of a new kind of ATPS compared with original aqueous solutions. At the same time the effect becomes more obvious when the chain length of alcohol is getting longer. However, the dihydric alcohols have little effect on the diagram of ATPS. Experimental results also show that the CMC of the mixed solution has something to do with the lowest concentration of surfactants under which the ATPS can form, but CMC is not the only factor.