Abstract: The nature and effect of coke formation on PtSn dehydrogenation catalyst were investigated by various technologies, such as HRTEM, XRD, FT-IR, Raman, ¹³C NMR, NH₃-TPD, DTG and ultimate analysis. The deactivation process of the catalyst was also discussed. The results showed that the catalyst deactivation was mainly caused by deposited carbon, which covered active sites and blocked the pores of the catalyst. The diffraction peaks of the amorphous graphite carbon were observed in the XRD patterns of the fully deactivated catalyst. Furthermore, the degree of aromatization and graphitization of coke formed in the catalyst were enhanced. It was difficult to regenerate the deactivated catalyst through coke elimination. It is proposed that the carbon deposit proceeded on the Pt active site by propane deep dehydrogenation and the deposited carbon could transfer to the surface of the support. The coke precursor is probably C₂₄H₁₂ when the coke content was accumulated to a certain degree.