Abstract: Phloroglucinol-melamine-formaldehyde polymeric nanofibers (PMF) were hydrothermally synthesized by a polycondensation method using melamine, phloroglucinol and formaldehyde as starting materials. The effect of temperature on the PMF synthesis was investigated. The morphology and structure of the as-synthesized PMF were characterized by the scanning electron microscope (SEM), transmission electron microscope (TEM), N₂ adsorption-desorption and Fourier-transform infrared spectrometer (FT-IR) etc. Pure gas adsorption equilibrium isotherms of CO₂ and N₂ were determined by the volumetric method. The PMF sample synthesized at 393 K presented a higher specific surface area (64 m²/g) and a higher adsorption capacity of CO₂ (1.83 mmol/g@118 kPa, 298 K). Breakthrough column experiments indicated that efficient separation of CO₂-N₂ mixtures could be achieved on the PMF at 298 K and various pressures ranging from 200 to 600 kPa. After the PMF was thermally treated at 873 K in various atmospheres such as N₂, H₂, water vapor, etc., it was found that the specific surface area and micropore volume were greatly increased. Among the posttreated PMF samples, the one treated in 15% H₂O stream showed an improved CO₂ adsorption amount up to 2.83 mmol/g at 298 K and 118 kPa.