Objective To observe the adhension and stracking of leukocyte in the capillary vessels, and investigate the relationship between leukocyte and microvascular morphologic changes in retinal microvessels of rats with early diabetes. Methods A total of 90 healthy adult male Wistar rats were randomly divided into control and diabetes (induced by Streptozotocin, STZ) groups with 45 rats in each group. The rats in the diabetic group were further divided into 3, 7, and 14 days groups with 5 rats in each group, and 30, 90, and 180 days groups with 10 rats in each group. The right eyes of rats in each group were prepared for retinal digest preparations. The expression of leukocyte common antigen (CD45) was detected by immunohistochemical staining. Results Few CD45 positive cells in the retinal capillaries were seen in the control group. The expression of CD45 was significantly increased in the retinal capillaries 3 days after diabetes induction, and reached a peak at the 14th day. Morphological changes including capillary telangiectasia, atresia, and irregularity of capillary caliber were found in the retinal capillaries of rats 90 days after diabetes induction. The changes were aggravated 180 days after diabetes induction. Conclusion Leukocyte adhesion occurs in the early stage of diabetic retinopathy (DR), and is the beginning of the microvascular pathological changes. Leukocyte adhesion may play an important role in the occurrence and development of DR as the foundation of microvascular morphological changes.