High signal-to-noise surface enhanced Raman scattering (SERS) signal of rat serum was obtained in this article. Two methods were presented to enhance the intensity of rat serum SERS signal. The novel colloid silver was synthesized using heating method by microwave and it was introduced to be the active site of SERS, "hot sites" could be detected in the active site. At same time the high numerical aperture (NA) oil immersed object lens was applied in micro-Raman system so that some new peaks come up in SERS spectrum of rat serum because of the evanescent wave was employed to excite the sample.