The spectrophotometric and electrochemical properties of tetraazo(p-carboxy)phenylcalix[4]arene (p-CAC) in the presence of various metal ions were investigated by UV/Vis spectroscopy and voltammetry in CH3CN. p- CAC showed selective color changes to Cu2+ over other metal ions from light orange to colorless, in accordance with hypsochromic shift in UV/Vis spectra. Voltammetric measurements also showed high selectivity for Cu2+.