3,5-O-di-galloylquinic acid (DGQA) purified from leaves of Myrtus communis was investigated for its antioxidative, antiproliferative and antigenotoxic activities. Antioxidant activity was determined by the ability of the compound to inhibit lipid peroxidation induced by H2O2 in the K562 cell line. The pure molecule displayed an important malondialdehyde formation inhibition percentage (82.2%). Moreover, this compound exhibited an inhibitory effect against H2O2-induced genotoxicity, using the comet assay. A protective effect of the same molecule was also revealed when assessing the gene expression of the chronic myelogenous leukemia cell line (K562), stressed with H2O2. For this purpose, we used a cDNA-microarray containing 82 genes related to cell defense, essentially represented by antioxidant and DNA repair proteins. We found that DGQA increase the activity of antioxidant enzymes family and the activity of DNA repair enzymes. Taken together, these observations provide evidence that the DGQA is able to protect cells against oxidative stress.