Metformin drug has a widespread usage in diabetes mellitus , it prevents hepatic glucose release and increases tissue insulin sensitivity. Metformin toxicity is established in metabolic failure of liver and kidney disorders, Lactic acidosis toxicity induced by metformin, may lead to central nervous system dysfunction, cardiovascular collapse, renal failure, and death. The studies investigated the genotoxicity of metformin are few either in vivo and in vitro and are controversial. The possible cytotoxicic and mutagenic effects that may be induced by metformin had been investigated in vitro models and compared it with the standard cytotoxic drug , cyclo phosphamide. Metformin did not cause an obvious genotoxic effect or increased oxidative stress and this was indicated by absence of changes in malondialdehyde( MDA), 8-hydroxy-2-deoxy Guanosine (8-OH-dG) levels and reduced glutathione (GSH) as compared to control normal group. So ,metformin did not cause any cytotoxic effect on comparing with the standard cytotoxic cyclophosphamide drug .Metformin does not express in vitro toxic effects .