The present study aimed to investigate the protective effect of yeast against mycotoxicosis induced by Aspergillus parasiticus and Fusarium tricinctum as common fungal contaminants on albino rats. 60 albino rats were randomly divided into three experimental groups: (A, B and C), each contain 20 animals. Group A: rats were kept as a control group was feed on uncontaminated feed and drinking water without any treatments. Group B: animals were feed contaminated diet with aflatoxins in level of 0.5 mg/kg ration and diacetoxyscirpenol in level of 10mg/kg ration. Group C: animals were feed contaminated diet as in group B. mixed with Saccharomyces cerevisiae (2g/kg of feed) during the whole time of the experiment. At the end of 1^st, 2^nd, 3^rd, and 4^th month, respectively, five animals from each group were weighted and dissected. Tissue samples were obtained from liver, kidneys and intestine for histopathological examination by light and electron microscope. The rats showed reduction of body weight and weight gain in group B. Addition of yeast to contaminated diet in the group C improved this reduction. Histopathological and ultrastructural studies revealed pathological changes in liver and kidney in group B. administration of yeast improve the intensity and the prevalence of the lesions and enhances the immune response of the body against mycotoxicosis (Lymphocytes and plasma cells).