In this study, mechanical, thermal and rheological properties of vulcanised ethylene propylene diene monomer (EPDM) rubber containing different amounts of vulcanising agent, filler, paraffinic oil and stearic acid were compared. Moreover, reaction rate constant of the curing reaction has been calculated from the results of the rheological tests, and relative change of rate constant with the change of additives was studied by a new method. Thermal gravimetric analysis with in situ Fourier transform infrared (FTIR) spectra was taken, and the thermal degradation of the EPDM rubber was observed for varying amounts of vulcanising agent and filler content. Although the vulcanising agent improved the mechanical properties of the EPDM initially, a further increase in the vulcanising agents deteriorated the mechanical properties. Attenuated total reflectance FTIR spectrum confirmed the decrease in the relative degree of cross-linking with the increase in the vulcanising agent content to 10 h(-1). Moreover, attenuated total reflectance FTIR spectra reaffirmed that cross-linking density increases with carbon black content. In situ FTIR spectra showed that the thermo-oxidative stability increased with the increase in filler content.