Objective To observe the ultrastructure of theca interna of the de-endothelium allogenetic blood vessels in dogs by transmission and scanning electron microscope at different phases. Methods The endothelium of the allogenetic blood vessels were first removed and cryodensiccated, and were then end to end anastomosed to canine femoral artery. Samples were collected and observed with scanning and transmission electron microscope on the first, second, fourth, eighth, twelfth, sixteenth, and twentieth week after transplantation, respectively. Results A layer of cellulose membrane was formed on the surface of allogenetic blood vessels one week after transplantation; Fusiform cells were observed at the anastomotic stoma of the allogenetic blood vessels two weeks after transplantation, and theca interna, which was covered by fusiform cells and elliptical erythrocytes, was formed twelve weeks later; Slightly hyperplastic smooth muscle cells and collagenous fibers were observed under the endothelium twelve to twenty weeks after transplantation. Conclusion The endothelium cells could cover the surface of the allogenetic blood vessels without remarkable hyperplasia of intima during a short period of time, which may suggest the satisfactory histocompatibility of canine allogenetic blood vessels.