Simultaneous thermogravimetry-differential thermal analysis and photoionization mass spectrometry (TG-DTA-PIMS) instrument connected with a skimmer-type interface has been successfully developed. Vacuum ultraviolet light used as a photoionization (PI) source provides an efficient and fragment-free method for soft ionization of gaseous organic compounds. In addition to this advantage, a real-time monitoring analysis of activated pyrolysates can be performed because transformation of the evolved gaseous species is suppressed by the skimmer-type interface, and fragmentation during ionization can be avoided with PI. These features permit a better understanding of the thermal behavior and the precise pyrolysates of polymeric materials. The pyrolysis of various standard reagent polymers such as Nylons, poly(methyl methacrylate) and polyethylene have been examined in a helium atmosphere. The synergy effect of the skimmertype interface and PIMS was evaluated and compared with conventional electron ionization MS results. The pyrolysates observed in the mass spectra consisted of only the parent ions. It was confirmed that the real-time monitoring PIMS worked satisfactorily. A valuable application of TG-DTA-PIMS is in fingerprint analyses of unknown commercial polymers. The results were compared with the PI mass spectra obtained from the pyrolysis of standard reagent polymers. Keywords: TG-DTA-PIMS, photoionization, VUV, soft ionization, fragment free, polymer degradation, skimmer interface