The effects of Ca^2+ ion on the formation of micelle colloid of nonionic surfactants, nonylphenol-(ethylene oxide)_n [NP-(EO)n; n=11,40,100) were investigated by the iodine solubilization method. The characteristics of spectra depended on the concentration of Ca^2+ ion and the number of EO unit. Above CMC(critical micelle concentration), the intensity of the CT (chargetransfer) band by the addition of Ca^2+ ion for the NP-(EO)_11 and NP-(EO)_40 increased and then decreased and for the NP-(EO)_100 continuously increased. The increase in the intensity of CT band were attributed to the compactness of micelle in the presence of Ca^2+ ion. These phenomena mad be explained by the fact that the linear ethylene oxide (EO) chain, relatively free to assume various configuration in aqueous solution, could form a pseudo-crown ether structures capable of forming complexes with Ca^2+ ion.