Composites based on ethylene propylene diene rubber (EPDM) loaded with different contents of flax fibers were irradiated using accelerated electron beams at various irradiation doses (75, 150, 300, and 600 kGy). The mechanical, physical, thermal properties, and morphology were analyzed as a function of e-beam irradiation dose and natural fiber loading. Also, crosslink density, gel fraction, and water uptake were investigated to characterize the EPDM/fiber composites subjected to e-beam irradiation. It was noted that the irradiation dose had a positive influence on hardness, 100% modulus and tensile strength, but an inverse effect was found on the elongation at break and elasticity. The crosslink density was estimated based on equilibrium solvent-swelling measurements using the Flory-Rehner relation. The kinetic parameters of thermal decomposition were determined applying the Flynn-Wall-Ozawa isoconversional method.