This article reports the thermal and fire behaviors of a high performance polymer, namely polyimide (PI). These behaviors were investigated using different techniques and tests, i.e., pyrolysis-Gas-Chromatography/MassSpectrometry (py-GC/MS) and TGA coupled with a Fourier Transform InfraRed spectrometer (TGA-FTIR), and mass loss cone (MLC) at different heat fluxes. It was observed that the thermal stability of PI strongly depends on the oxygen concentration. The main identified gases released during thermal degradation are: carbon dioxide, carbon monoxide, water and organic compounds (phenol, aniline, cyanobenzene, dicyanobenzene, 4-aminophenol, benzene, 2-(4-hydroxyphenyl)isoindoline-1,3-dione, phthalimide, dibenzofuran, and diphenylether). The ignition of PI in MLC experiment is observed under an external heat flux of 60 kW/m2. In that case, the peak of heat released by polyimide is only 30 kW/m2. Based on these investigations, a possible decomposition pathway of PI is proposed.