The aggregation behavior in binary mixtures of two surfactants, 1-hexadecyl-3-methylimidazolium chloride and dodecyltrimethylammonium bromide, has been investigated in aqueous solutions using conductometric, tensiometric, spectrofluorimetric, and zeta potential measurements. The counterion binding, aggregation number, and anisotropy of the micellar environment have been ascertained. The results have been analyzed on the basis of the theories of Clint, Rubingh, and Motomura. The thermodynamic parameters of the micellization process have been evaluated and discussed. The interfacial adsorptions of the mixed surfactants including their surface excesses and headgroup areas have also been evaluated. The existence of an attractive interaction among the constituents of the mixed surfactant systems investigated has been inferred.