Glutaredoxins (GRXs) are small proteins with glutathione-dependent disulfide oxidoreductase activity involved in cellular defense against oxidative stress. This work reports the identification and characterization of the first glomeromycotan dithiol glutaredoxin gene from the fungus Glomus intraradices. The corresponding gene, named GintGRX1, shares high sequence similarity with previously described fungal GRXs. GintGRX1 contains the characteristic dithiol active site CPYC. By using a yeast expression system, we found that GintGRX1 encodes a multifunctional protein with oxidoreductase, peroxidase and glutathione S-transferase activity. GintGRX1 partially reverted sensitivity to superoxide radicals of the Deltagrx1Deltagrx2Saccharomyces cerevisiae strain. GintGRX1 was transcriptionally regulated by paraquat but not by hydrogen peroxide. Copper induced an accumulation of reactive oxygen species in the extraradical mycelium of G. intraradices and up-regulation of GintGRX1 transcript levels. These data suggest a role for GintGRX1 in protecting the fungus against the oxidative damage induced directly by the superoxide anion or indirectly by copper.