Abstract: The synergistic effect of three binary mixtures of nonionic/anionic surfactants including coconut oil ethoxylate(COE-30)/sodium linear alkylbenzene sulfonate(LAS), coconut oil ethoxylate(COE-30)/sodium alcohol ether sulphate(AES-2) and coconut oil ethoxylate(COE-30)/fatty alcohol ether carboxylates(AEC-5) was investigated. Non-ideal solution theory was used to determine the composition of the two components and the synergistic parameters in both mixed micelle and mixed absorption monolayer. The data indicated there is relatively strong synergistic effect in three binary systems. The synergistic parameters in mixed micelle and mixed absorption monolayer range from -6 to -3. The three blending systems exhibit synergistic effect in surface tension reduction efficiency and capacity for formation of mixed micelles, COE-30/AES-2 and COE-30/AEC-5 systems exhibit synergistic effect in surface tension reduction capacity as well.