This study aimed to investigate effects of diets containing two levels of red onion peels (ROP) and bread fortified with these peels on nutritional evaluation, some biochemical parameters, and histopathology of livers in rats suffering from diabetes mellitus. Forty-eight male Albino rats were used in this study. The rats were divided into two main groups as follows: The first main group of 12 rats was divided into two subgroups as a follow: Subgroup (1): fed on a basal diet and used as a negative control group. Subgroup (2): fed on a diet containing 250 g of unfortified bread/kg of diet and kept as a control negative group. The second main group: (36 rats) was subcutaneously injected with 120 mg/kg Alloxan monohydrate to induce hyperglycemia. The rats in the second main group were distributed into six equal subgroups as follows: Subgroup (1) was fed a diet containing 250 g of unfortified bread/kg of diet (as a positive control group). Subgroups (2) and (3) were fed diets containing the best two samples from bread estimated by the sensory evaluation (250) g and fortified bread with 10% and 15% of ROP/kg diets, respectively. Subgroup (4) was fed a basal diet (as a positive control group). Subgroups (5) and (6) were fed diets containing the levels of ROP present in 250 g and fortified bread with 10% and 15% ROP/kg diet, respectively. The results indicated that Alloxan increased liver weight/body weight percent, serum result revealed that glucose and most lipid profiles decreased feed intake, body weight gain%, and high-density lipoprotein-cholesterol. Treating diabetic rats with diets containing fortified bread with two levels of ROP (10 and 15%) and also the peels used in preparing this bread improved all of these parameters and ameliorated histopathological lesions seen in the liver as compared to non-treated diabetic rats. Conclusion: Red onion peels (ROP) and bread fortified with these peels can be used to reduce the side effects of diabetes mellitus in diabetic rats. Therefore, intake of ROP may be beneficial for diabetic patients.