The voltammetric study on a water-soluble calix[4]arene (calix[4]arene-triacid-monoquinone, CTA) in basic aqueous solution in the presence of Ca2+ ion provided important information about the unique electrochemical behavior of Ca2+-CTA complex. The redox behavior of CTA and voltammetric responses to Ca2+ ion are reminiscent of those of quinone-derivatized calix[4]arenes in aprotic media. Using CTA, Ca2+ ion in aqueous solution could be recognized quantitatively by voltammetric techniques.