The purpose of the present study is to evaluate the effects of either vitamin D or coconut oil or both together on the histological changes of the thyroid glands of diabetic adult male mice (Mus musculus) induced by using streptozotocin (STZ). The mice were divided into 7 equal groups (10 mice/each). The duration of the experiment was 4 weeks. Group I: normal control mice, a group without any treatments. Groups II and III: non-diabetic mice groups received vitamin D orally in a daily dose of 500 IU (6.25 ml/kg body weight) or coconut oil (7.5 ml/kg body weight/day), respectively. Group IV: diabetic mice group injected intraperitoneally with a single dose of STZ dissolved in saline solution in a dose of 200 mg/kg body weight to induce diabetes. Groups V, VI and VII: diabetic mice administered orally with vitamin D or coconut oil or both together with the same previous doses. The results recorded non-significant changes in the blood glucose, insulin levels of non-diabetic mice groups received either vitamin D or coconut oil. A high significant increase in blood glucose level and a significant decrease in insulin were found in the diabetic mice group as compared to the normal control ones. Diabetic mice group received the vitamin D only recorded a slight decrease in blood glucose level and a slight increase in insulin; while the diabetic mice received coconut oil alone or co-administered with vitamin D recorded a significant decrease in blood glucose levels and a significant increase in insulin as compared to diabetic group. Histologically, the mice of normal control group or that received either vitamin D or coconut oil showed the normal structure of thyroid follicular cells. Each follicle consists of a layer of simple cuboidal epithelial cells with spherical densely-stained nuclei, and its cavity contains vacuolated acidophilic colloid. The diabetic mice demonstrated many histopathological changes in the thyroid included vacuolated thyrocytes, enlargement of numerous follicles that were filled with colloids, and others demonstrated fusion between them. The appearance of dilated and congested blood vessels in the interstitia between the follicles was also seen. The diabetic mice administered with vitamin D elucidated little improvement in the thyrocytes, while that received either coconut oil alone or co-administered with vitamin D illustrated a marked recovery in the structure of  the thyrocytes with normal nuclei similar to the control form. In conclusion, diabetic mice received either coconut oil alone or co-administered with vitamin D demonstrated stronger anti-hyperglycemic effects to recovery the glucose and insulin rates to normal levels, and restored the histological architecture of the thyroid glands to approximately the normal status than those given vitamin D only.