An investigation on Surface Plasmon Resonance (SPR) based fiber optic sensor for mercury detection utilizing copper-silver core shell nanoparticles (Cu@Ag CNPs) was carried out. TEM analysis was used to confirm the formation and morphological characteristics of the CNPs, whereas EDS and AAS analysis were used to validate the successful formation of the core shell nanoparticles. Good selectivity and sensitivity towards mercury were established by means of UV-Vis absorption spectroscopy. SPR based fiber optic mercury sensor was fabricated using Cu@Ag CNPs as the sensing materials and the results clearly prove that the Cu@Ag CNPs can act as suitable candidates for the same.