Calixarene functionalized gold nanoparticles (CFAuNPs) have been prepared and characterized by spectroscopic and microscopic (TEM) techniques. To use this material as potential colorimetric sensor, the binding property of this new material has been investigated with a large number of metal ions. It exhibited sharp colour change from dark brown to green and blue, detectable by naked-eye, in the presence of Cu²⁺ and Pb²⁺ ions, respectively. It has also triggered substantial change in surface plasmon resonance (SPR) band of the functionalized gold nanoparticles, which in case of Pb(II) is due to the inter particle plasmon coupling arising from the metal-induced aggregation of the nanoparticles and for Cu(II), it is because of the formation of AuCu alloy due to anti-galvanic exchange. The size and aggregation of the nanoparticles are confirmed from HRTEM images, elemental analysis and the line profiling for both the metal ions have been done by STEM-EDX analysis.