Genotoxic effects of the mycotoxin Zearalenone (ZEN) were evaluated on albino mice. The investigation was assessed using 4 criteria: chromosome aberrations in bone marrow and sper- matocytes of adult male mice; chromosome analysis and teratological effects of mice embryos. Zear- alenone was administrated to both adult males and pregnant females with 2 doses level (5 μg.kg -1 and 10 μg.kg -1 ZEN). Zearalenone was found to reduce the mitotic activity in treated males and the embryos proving that it is a cytotoxic substance. In treated males and females, it induced some chro- mosome abnormalities with no significant increase over the control at the doses investigated, except for some few figures. Similar results were observed for the teratological study. The results in general could consider zearalenone as a toxic mycotoxin for both adult animals and embryos. It is highly rec- ommended that a great attention should be paid towards the toxicity of zearalenone to mono-gastric animals and human, especially it contaminate corn that is widely used in human and animal feeding. genotoxicity / zearalenone / mice / embryo / chromosome / spermatocyte