CD34 is expressed in various cell types in various tissues/organs, and has been regarded as being expressed in progenitors in various differentiation pathways. On the other hand, morphological studies have reported the presence of a special type of interstitial cells, telocytes, which generally express CD34, and have extremely long moniliform prolongations in various tissues/organs in vertebrates. We have recently reported the successful reconstruction of testicular structures by 3-D re-aggregation culture of dissociated prepubertal mouse testicular cells, and the roles of CD34 ⁺ cells in the reconstruction. However, it was unknown whether CD34 is expressed in embryonic through adult testes, and if so, in what cell type it is expressed. In order to clarify the expression of CD34 and behavior of CD34 ⁺ cells during development of mouse testes, we performed immunohistochemical studies. The results show that CD34 is expressed in two cell types in testes; one is endothelial cells which co-express CD31, VE-cadherin, and integrin β1, but barely express PDGFRα and integrin α4 and α9, throughout development, while the other one is non-endothelial cells in which CD34 expression is initiated after birth, and which co-express PDGFRα and integrin α4, α9, and β1. The latter corresponds to telocytes. The present findings will lead to clarifying the roles of these two types of CD34 ⁺ cells in spermatogenesis.