The interfacial diffusion of yttrium stabilized zirconia (YSZ)-samarium, neodymium co-doped ceria (SNDC) bilayer electrolyte has been systematically investigated by laser confocal micro Raman spectrometer. The bilayer structured electrolyte prepared using conventional sintering (CS) and spark plasma sintering (SPS) are well densified according to SEM measurement. Raman mapping clearly displayed the diffusion boundary of two layers by using the intensity of peak at 465 cm(-1). We probed the concentration change of CeO2 across the interfacial region and figured out the diffusion thickness of specimens, based on the change of Raman spectroscopy at different positions. This result agrees quite well with the one obtained through EDS. The reliability of diffusion thickness on the sintering temperature and holding time was discussed according to Fick's law.