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 (charge transfer) band by the addition of $Ca_{2+}$ ion for the NP-(EO)11 and NP-(EO)40 increased and when decreased and for the NP-(EO)In 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 may 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.