Objective: For the purpose of understanding the changing process of syphilis histomorphology and its injury mechanism,the ultrastructure of dermatic tissues of secondary syphilis was studied.Methods: Different skin injury tissues of secondary syphilis patients, whose serum RPR and TPHA tests in the lab both appeared positive reaction, were observed through transmission electron microscope (TEM).Results: Inflammations appeared on epidermides and coria,a great deal of neutrocytes, lymphocytes and a small amount of plasma infiltrated them. Karyopyknosis, karyorrhexis,epicyte lysis and mitochondrion vacular degeneration occurred. Spirocheta pallida was distributed on intercellular substances, epicytes and coilagenous fibers. The epicytes were pressed to foveation. Conclusion The pathological change of characteristic tissue ultrastructure reported here is a histomorphological foundation to study the organism injury mechanism caused by syphilis.