This work was aimed at studying supercritical carbon dioxide (scCO(2))-induced melting temperature depression and crystallization of a syndiotactic polypropylene (sPP). Under scCO(2), the melting temperature of the sPP could be significantly reduced depending on the CO2 pressure. The scCO(2)-induced crystallization of sPP was investigated using differential scanning calorimeter (DSC) and Fourier transform infrared spectroscopy. Two melting peaks were observed in DSC. The one at lower melting temperature referred to the melting of the sPP crystals induced by scCO(2) in its amorphous phase. Its location was shifted to higher temperature, and its area increased with increasing scCO(2) treatment time, temperature, and pressure. The melting peak at higher temperature corresponded to the melting of the sPP crystals that already existed before scCO(2) treatment. Its location and area remained almost unaffected by the scCO(2) treatment. The scCO(2)-induced crystallization was related to scCO(2)-promoted transformation of the mesophase form III of the sPP to the stable form I.