We proposed and developed a novel fiber-optic biosensor based on localized surface plasmon coupled emission (LSPCE) which consists of sandwich format of 〈antibody/antigen/Cy5-antibody-GNP〉 immuno-complex. It is immobilized on the surface of optical fiber where 〈Cy5-antibody-GNP〉 is a fluorescence probe produced by mixing Cy5 labeled antibody and protein A conjugated gold nanoparticles (Au-PA). The fluorophores are excited by localized surface plasmon (LSP) on gold nanoparticle (GNP) surface where the evanescent field is applied near the core surface of unclad optical fiber. Meanwhile, the fluorescence signal is detected by a photomultiplier tube being set beside the unclad optical fiber with high collection efficiency. In the experiment, this novel LSPCE biosensor demonstrates the minimum detectable concentration of mouse immunoglobulin G (IgG) at 1pg/ml (7fM) in the biomolecular interaction with anti-mouse IgG. From the experimental result, it verifies that LSPCE biosensor is a very high sensitive biosensor which is capable of measuring biomolecular interaction at very low concentration.