Micellization behavior of cationic monomeric surfactants, hexadecyltrimethylammonium bromide (CTAB), cetylpyridinium bromide (CPB), cetylpyridinium chloride (CPC), tetradecyltrimethylammonium bromide (TTAB), and dimeric (gemini) cationic surfactant pentamethylene-1, 5-bis(hexadecyldimethylammonium bromide) with formula C16H33(CH3)(2)N+(CH2)(5)N+(CH3)(2)C16H33 center dot Br-, abbreviated as 16-5-16, in mixed states (binary) have been studied by conductivity. The micellar compositions, activities of the components, and their mutual interactions have been estimated from Rubingh's theory. The mixtures show nonideal behavior with favorable interactions.