Aflatoxin B1 (AFB1) is a fungal toxic secondary metabolite produced by Aspergillus flavus and Aspergillus parasitic us in different agricultural commodities. Presence of (his toxin in food and feed causes great economic loses and health hazard to human and animal. This work covers some chromosomal variations caused by AFBi such as gap and break chromosome, gap and break chromatic! , dicentric chromosome, acentric chromosome, and ring chromosome. In addition to the in vitro, the study also included the in vivo aspects through applying different doses of AFBi (0.2 , 0.1 , 0.01 ppb/ mouse) to mice, and ( 0.5 , 0.2 , 0.1 , 0.01 ppb/ ml) to human blood culture . Both mice and human treated with 4ug /ml of mitomycin-C (MMC)and 0.1 of 50 % ethanol doses for comparison. The following results were obtained:- 1- The AFB1 showed high toxicity effect on the phenotypic properties of the mouse, on its manner and its normal activities. 2- A dose dependent cytotoxic effect of AFB1 (especially at concentration of 0.2ppb) was observed on spleen and bone marrow cells of mice which included many chromosomal aberrations such as (chromosome gap and break, chromatid gap and break, dicentric chromosome, acentric chromosome, and ring chromosome). 3- A dose dependent cytotoxic effect of AFB1 (especially at concentration of O.Sppb) was also recorded on human blood lymphocytes including (chromosome gap and break, chromatid gap and break, dicentric chromosome, acentric chromosome, and ring chromosome). Multiple chromosomal aberrations (CA) in the same cell in both mice spleen and bone marrow cells and human blood lymphocytes cells were detected due to Aflatoxicosis. The levels of the enzymes GOT and GPT were changed in the treated animals indicating the effect of the toxin on the liver functions , while there was a very slightly effect of AFB1 on the level of ALP enzyme were observed .The effect of AFBi1on the liver function was dose dependent