Mechanical degradation of rubber significantly affects its performance and lifetime, making it a critical factor in the field of industrial applications [1]. Ethylene-propylene-diene terpolymer (EPDM) rubber is widely used in automotive parts and industrial seals due to its chemical resistance and flexibility. However, it is susceptible to abrasive degradation, so tracking this process, especially in real time, is crucial. Radiolabelling EPDM with gamma emitting radioactive isotopes offers a powerful analytical method to trace and monitor this degradation, as even minimal radiotracer amounts may still enable easy and precise detection [2,3]. In this study, Ru-103 was selected based on its suitable half-life (~ 40 d) and gamma emission (497 keV, 91 %) properties. The radiolabelling process was conducted by diffusing gaseous Ru-103 labelled ruthenium(VIII) oxide into the EPDM matrix. Subsequent reaction with unsaturations within the rubber immobilizes the ruthenium-based tracer. Gamma spectrometry and autoradiographic methods were employed to confirm the successful incorporation, assess spatial distribution of the radiotracer within the EPDM matrix and confirm irreversibility of the labelling process. Gamma spectroscopic and autoradiographic results affirm that EPDM can be very effectively radiolabelled, and the amount of radioactivity within the rubber can be evaluated and controlled by several different parameters. Labelling depth is controlled principally by exposure time (to RuO 4) and the distribution of Ru-103 in the labelled EPDM is very nearly homogeneous (no measurable concentration gradient). To ensure that the radioactivity is not confined to surface deposition, solvent (acetone) treatments using ultrasonic cleaning procedures were performed, and the spatial distribution of the activity inside the rubber was visualized showing minimal loss of activity on treatment. Further research will focus on characterizing and quantifying the diffusion of Ru-103 into the crosslinked rubber matrix at the molecular level. [1] D. Stamenkovic et al, Tribol Ind 2014, 36, 9-16 [2] J. Sterba, J. Radioanal. Nucl. Chem. 2018, 316, 753-759 [3] G. Steinhauser et al, Environ Sci Pollut Res Int 2013, 20, 2527-2534