A highly sensitive immunoassay based on surface enhanced Raman scattering (SERS) has been developed with a novel immune marker named as Raman reporter-labeled immuno-Au aggregates on a SERS-active immune substrate. The features of those immune aggregates were characterized by UV-vis extinction spectra, TEM images, SEM pictures and SERS spectra. It is found that stable gold aggregates in appropriate morphologies can be induced by mixing proper amounts of reporter molecules with gold nanoparticles. Based on those reporter-labeled Au aggregates, the immune aggregates with high stability can be prepared successfully by immobilizing antibody to the surface of the aggregates. Using those easily prepared aggregates showing strong SERS activity and high bio-specificity, a highly effective SERS-based immunoassay has been performed. Moreover, a SERS-active immune substrate has been introduced to replace a typical immune substrate without any SERS activity. Our experimental results indicate that the SERS-active immune substrate makes a certain contribution to the highly sensitive immunoassay. As a result, with this proposed immunoassay structure, the concentration detection of human-IgG was performed and a calibration curve was obtained in the range from 100ngmL(-1) to 100fgmL(-1). This work opens a new avenue for sensitive immunoassay and other biochemical analysis based on SERS.