Stress relaxation rate in unirradiated and electron-beam-irradiated polycrystalline titanium (99.994%) was studied in the temperature range 300–100 K. Titanium specimens were irradiated with 12 MeV electrons to a dose of 0.01 dpa for 12 min. at 300 K. Tensile tests of the specimens were performed using a Universal Testing Machine in the given temperature range. To measure the relaxation of stress with time, the crosshead of the machine was arrested at different fixed loads. Stress relaxation rate s for a given stress level σ0 was found to be temperature dependent, i.e., it decreased with decreasing temperature both in unirradiated and irradiated specimens. However, the decrease was more pronounced in irradiated specimens than that of unirradiated ones. The observed decrease in s values with decrease in temperature is ascribed to the retarding effect of unrelaxed dislocations pinned at defects, especially at the twin boundaries in the course of deformation, which became more conspicuous in irradiated specimens due to the interaction of glide dislocations with radiation-induced defects, in addition to mechanical twins. The activation energy for the movement of dislocations, calculated using the single-barrier model of stress relaxation, was found to be higher in irradiated specimens than that of unirradiated ones at all test temperatures. [ABSTRACT FROM AUTHOR]