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