Heavy metal emissions in the environment increase due to the rapid development of technology. The measurement of heavy metals with high accuracy and precision is the most important mission of analytical chemistry. Cadmium is a heavy metal that poses an environmental hazard. It is non-biodegradable and toxic to plants, animals, and human beings. It causes various types of acute and chronic disorders. Therefore, the removal of Cd(II) ions from aqueous solutions are needed. The adsorption of Cd(II) ions on functionalized multi-walled carbon nanotubes (MWCNTs-COOH) from aqueous solutions was optimized using a response surface methodology (RSM) based on a central composite design (CCD). The effects of three variables initial pH, initial concentration of cadmium, and temperature on the amount of adsorbed Cd(II) (q) (as a response) were investigated. pH was found as the most significant factors that affect the removal of Cd(II). This study has shown that CCD is an economical way of obtaining more information with a minimum number of experiments for the removal of Cd(II) ions from aqueous solutions.