The transitions in bitumen in the temperature range of 25–75 °C are normally investigated using rheological tools. Considering the complex response of the material in such temperature range, it will be helpful if the precise nature of the material is investigated at the macromolecular level also. In this study, an attempt is made to use FTIR spectroscopy to identify the thermal transitions in unmodified and three modified bitumen. The changes in peak position and intensity of the C–H stretching vibration at 2953, 2923 and 2853 cm −1 were analyzed. Transitions, predominantly solid–solid in nature were identified in the temperature range of 35–65 °C which can be attributed to the change in conformation of the crystalline fraction. While certain peaks distinguished the effect of modification and aging, few other peaks indicated multiple transitions in the solid state of the material. The degree of crystallinity, also calculated from the FTIR spectra, indicated changes in the conformation of the material in the temperature range of 45–55 °C. © 2019, RILEM.