Poly(3,4-ethylenedioxythiophene)/Poly(styrenesulfonate) (PEDOT/PSS) is a widely used conductive polymer in the field of flex- ible electronics. The ways its microstructure changes over a broad range of temperature remain not well understood. This paper describes microstructure changes at different temperatures, and correlates microstructure with its physical properties (mechanical and electrical). We used High-Angle Annular Dark-Field Scanning Electron Microscopy (HAADF-STEM) combined with elec- tron energy loss spectroscopy (EELS) to determine the morphology and element atomic ratio of the film at different temperatures. These results together with the Atomic Force Microscopy (AFM) analysis, provide the foundation for a model of how temper- ature affects the microstructure of PEDOT/PSS. Moreover, dynamic mechanical analysis (DMA) and electrical characterization were performed to analyze the microstructure and physical property correlations