Aflatoxin BI (AFBi) is a toxic fungal secondary metabolite produced by Aspergillus flavus and Aspergillus parasiticus indifferent agricultural commodities like maize. The presence of this toxin in food and feed causes great economic loses and health hazard to human and animals. The aim of this study include the production of AFB1 on maize substrate as well as studying it's pathogenic effect and toxicity in rats. The results of the study revealed the following: 1- The isolate (BM1) was proved to be AFB1 producer on maize substrate, the amount of AFB1 produced by this isolate was 400.39 ppb. as estimated by scanning densitometer. 2-The use of crude AFB) or the diet contaminated with the spore suspension of the fungus caused pathological signs of marked increased in body weight, dyspanea, diarrhea, shivering, increase water and feed consumption, bristling up of hair and irritation around the neck. 3. The histopathological study involved the liver after one month of treatment with AFB1 by the light microscopic examination pointed many variation in liver include degenerative changes in hepatic cell, abnormal appearance of cytoplasm and nucleus, abnormal cellular mass in the liver structure with dilated sinusoid. 4. Ultrastructural study of liver by electron microscop revealed many changes in. the treated rats, the nucleus appeared with thick membrane in addition to microsome and fat droplet formation.