Background: CD93 has originally been known as a C1q receptor, and many studies have demonstrated that CD93 is expressed on hematopoietic stem cells, B cell progenitors, myeloid and monocytic cells. Moreover, CD93 is shown to be expressed on long-lived plasma cells, and CD93 deficient-mice display an impairment in plasma cell development. Objective: To investigate the expression of CD93 on multiple myeloma (MM) cells. Methods: Human MM and B cell lines were cultured, and the expression of CD93 was examined on these cells by quantitative Reverse Transcription Polymerase Chain Reaction (qRT-PCR) and Fluorescence Activated Cell Sorting (FACS). In addition, CD19+ primary B cells and CD19-/CD138+ primary MM cells were isolated by MACS columns, and CD93 expression was further analyzed on these cells. Results: qRT-PCR data showed that CD93 expression at mRNA level was much higher in MM cell lines compared with B cell lines. In addition, MM cell lines expressed a higher amount of surface CD93 at protein level compared with B cell lines. More importantly, CD93 expression was significantly higher in CD19-/CD138+ primary MM cells than in CD19+ primary B cells isolated from the bone marrow of patients with MM. Conclusion: We demonstrated that CD93 is expressed on myeloma cells and, that CD93 could play a key role in the pathogenesis of MM. Further studies are necessary to explore this possible role.