The present work was conducted to study the beneficial effect of different types of fish on diabetic rats and diabetic rats treated with insulin. This study investigated the chemical composition of four types of fish (Mackerel, Sardines, Smoked herring and Bolti) and also the effects of these types on the nutritional value and the levels of serum (glucose, lipid fractions, kidney and liver functions) of diabetic rats. The chemical composition "on dry bases matter" of processed fish types revealed that the bolti fish had the highly percent of protein, while the highest percent of fat was found in mackerel and sardines. The mackerel had the highest percentage of polyunsaturated fatty acid, followed by sardines, herring and bolti. Seventyfive male Albino rats used in this study, weighing (150 +/- 5 g) were divided into three main groups (n = 25). The first main group was considered negative control. The second main group was injected with 150-mg/kg-body weight of recrystallized alloxan to induce hyperglycemia. The third main group was injected with 150-mg/kg-body weight of recrystallized alloxan to induce hyperglycemia and treated with insulin injection. Each main group was divided into five subgroups. The first subgroup from each main group fed on a casein diet, while the second, third, fourth and fifth subgroups fed on basal diet containing mackerel, sardines, herring and bolti, respectively. Feeding diabetic rats with the different types of diet (fish diet) resulted in an improvement of the nutritional parameters. The mean values of serum glucose, cholesterol, triglycerides, LDL-c, HDL-c, VLDL-c, uric acid, urea nitrogen, aspartate amino transferase (AST) and alanine amino transferase (ALT) decreased in all treated groups especially with the mackerel and sardine diet, followed by bolti, as compared to the positive control groups (fed on a casein diet), while the levels of serum cholesterol and LDL-c increased in the groups fed on the herring diet. On the other hand, diabetic rats that were treated with a low insulin dose and fed on the mackerel diet, showed non-significant differences in the levels of all parameters, as compared to non-diabetic rats.