Abstract: Objective: To study the ultrastructural features and HLA-D antigen expression in the pathogenesis of arteriopathy of renal allograft.Methods: Intimal lesions in renal arteries from 5 allografts were embedded with K₄M and investigated by immuno gold electron microscope. The specimens of five normal donor renal artery served as control. Results: （1）There was aberrant expression of HLA-D antigen by both endothelial and smooth muscle cells of arteriopathy. （2）The main components of intimal lesion were the synthesized type smooth muscle cells, which characterized by abundant intracytoplasmic rough endoplasmic reticulum and c-myc gene protein expression, and their extracellular matrix. （3）About 65% of intimal inflammatory infiltrates were T lymphocytes and the other 35% were of macrophages. （4）The number of CD₄ lymphocytes were equal to that of CD₈ cells. The two subtypes of T lymphocyte shared similar morphologic features. （5）There was no CD₂₀ positive B lymphocyte in the intimal lesions.Conclusions:The arteriopathy of renal allograft is a T-lymphocyte-mediated endotheliolitis triggered by intimal endothelial injury. The cellular interactions through HLA-D antigen among T lymphocytes, macrophages, and smooth muscle cells may result in intimal proliferation and arterial stenosis.