Purpose: x-ray contrast agents that contain iodine are commonly used for interventional and diagnostic procedures. To progress selective x-ray imaging, and discriminate the attenuating media, it is important to determine the absorption edge values and absorption features of the compounds used as contrast agents. For this purpose, mu rho (mass attenuation coefficients), Zeff (effective atomic number) and Nel (electron density), which characterize the possibility of interaction with x-ray of iodine containing contrast agents (ICCAs: Iodixanol, Iohexol, Iopamidol, Iopromide, and Ioxagalete) were calculated using WinXCom code and Penelope Monte Carlo simulation programs. Materials and methods: Calculations were obtained in an energy range from 1keV to 1GeV. The values of Zeff and Nel were calculated using the mu rho values of compounds. Variation in mu rho, Zeff, and Nel values of the ICCAs were determined depend on x-ray energies. Results and discussion: It was determined that in the low energy region, where the probability of photoelectric absorption was high. In the intermediate energy region, where the compton scattering process occurs. Additionally, an increase was observed in the potential for pair production effect in the presence of high energy values. Moreover, since Z4-5 depended on the photoelectric effect, the cross-section significantly contributed to the Zeff values of the ICCAs; the highest values for Zeff and Nel were observed in low energy ranges. Furthermore, the results obtained from the two different code programs were similar to one another. Conclusion: The results of this study may be useful for determining the accuracy of the Zeff and Nel values of ICCAs using dual energy CT. As such, this research can contribute to developing a method for enhancing CT image quality.