The present study aims to study the effect of vitamin D (Vit. D) or/and coconut oil (C.O) on the splenic histological changes of diabetic adult mice induced by streptozotocin (STZ). The mice were divided into 7 groups (n=10), and the experimental duration was 4 weeks. Group 1 (GpI): control group without any treatment; GpII and GpIII: non-diabetic groups, orally received Vit. D in a dose of 500 IU (6.25 ml)/kg b.w/d or C.O in a dose of 7.5 ml /kg b.w/d, respectively; GpIV: diabetic group injected i.p. with a single dose of STZ (200 mg/kg bw). Gps V, VI and VII: administration of Vit. D or C.O or both together to diabetic group respectively. The results showed no significant changes in the blood glucose (BG), insulin, and splenic weight in GpII and GpIII. GpIV showed a significant increase in BG, significant decrease in insulin levels, and splenic weight values. GpV recorded a moderate decrease in BG, and a moderate increase in insulin levels and splenic weight atrophy. While GpVI or GpVII showed a marked decrease in BG and an increase in insulin levels and splenic weight increment. Histologically, the splenic sections of control or non-diabetic mice received either Vit. D or C.O showed normal structure of the splenocytes. GpIV showed great numbers of giant cells, disarrangement, interference of red and white pulps, and dilated congested blood vessels. Mild improvement was seen in GpV, while in GpVI or GpVII showed a marked improvement in the splenic tissues. In conclusion, diabetic mice received Vit. D/C. O showed strong anti-hyperglycemic effects to restore the glucose and insulin levels close to normal levels. It also restored the splenic weight and histological architecture close to normal status than those administered Vit. D alone.