In applications like space satellites, high-energy physics experiments, and nuclear power stations, epoxy structural adhesives are normally used in an ionizing radiation environment. To check the effects of γ-irradiation on room temperature epoxy adhesives, mechanical measurements were undertaken for three different resins up to the dose of 3 MGy. Both dumbbell and single-lap shear tests were performed. To correlate the measured radiation effects on these mechanical properties with the molecular modifications of the resins, outgassing and calorimetric tests were performed on one of the tested adhesives. As a result of these tests, the mechanical modifications were associated with the combination of reticulation, network scission, and production of low-weight molecules due to radiation. Differences in shear and tensile strength behaviors were associated with the presence of the adhesive-adherend interface.