Vanillic acid, a vegetable phenolic compound, is a strong antioxidant. The aim of the present study was todetermine its effects on mitomycin C-induced DNA damage in human blood lymphocyte cultures in vitro, bothalone and in combination with mitomycin C (MMC). The cytokinesis block micronucleus test and alkalinecomet assay were used to determine genotoxic damage and anti-genotoxic effects of vanillic acid at the DNAand chromosome levels. MMC induced genotoxicity at a dose of 0.25 μg/ml. Vanillic acid (1 μg/ml) significantlyreduced both the rates of DNA damaged cells and the frequency of micronucleated cells. A high dose of vanillicacid (2 μg/ml) itself had genotoxic effects on DNA. In addition, both test systems showed similar results whentested with the negative control, consisting of dimethyl sulfoxide (DMSO) in combination with vanillic acid (1μg/ml)+MMC. In conclusion, vanillic acid could prevent oxidative damage to DNA and chromosomes when usedat an appropriately low dose.