The effect of roasting coffee beans artificially contaminated with ochratoxin A (OTA) on its genotoxic properties was studied in Allium cepa. Green coffee beans, artificially contaminated with OTA, had an OTA concentration of 12 ng/g, and after roasting at 230 °C for 5, 8 and 12 minutes showed OTA concentrations of 9, 5 and 2.2 ng/g, respectively. OTA-non-contaminated coffee beans were used to compare the results. Based on the results from the Allium cepa test, ochratoxin proved to be toxic and genotoxic at different concentrations for meristematic cells. OTA-non-contaminated coffee beans also showed genotoxic effects. A. cepa species is an efficient test organism to assess the toxic effects induced by mycotoxins such as ochratoxin A. Genotoxicity analyses on meristematic cells of A. cepa indicated that the roasting process was not efficient enough for OTA degradation because  the clastogenic and mutagenic effects were not reduced. This shows that OTA-degraded compounds could have possibly combined with Coffea arabica compounds forming compounds toxic to vegetable cells. In the present study, this assumption is based on the transformation of OTA-non-contaminated coffee cell compounds during the roasting process, which is proved by their genotoxic effects on Allium cepa meristematic cells.