The translational machinery is particularly sensitive to oxidative stress. Using an in vitro translation system from a cyanobacterium, we have demonstrated that elongation factor G (EF-G) is the primary target of oxidation by reactive oxygen species within the translational machinery. In the present study, we examined the effects of the overexpression of EF-G on the tolerance of cyanobacteria to oxidative stress. Overexpression of EF-G enhanced protein synthesis under oxidative stress and, moreover, mitigated the photoinhibition of photosystem II (PSII). It appears that increased levels of EF-G might minimize oxidative damage to protein synthesis and accelerate the repair of photodamaged PSII.