In erectile dysfunction (ED) research, monocultures of cavernous endothelial cells (CECs) and smooth muscle cells (CSMCs) have been reported, but a CEC-CSMC coculture system is still lacking. In the present study, we wished to investigate the feasibility of setting up such a system and test whether it can be used for diabetic ED research. Cavernous tissues were obtained from patients undergoing surgery for penile prosthesis. CSMCs were isolated by explant culture and verified by calponin staining. CECs were isolated by binding to CD31 antibody, followed by magnetic capture. These CECs were nearly 100% pure endothelial cells as determined by flow cytometric analysis for endothelial markers CD31, vWF and eNOS. Functional analyses, that is, low-density lipoprotein (LDL) uptake and capillary tube formation, also confirmed their endothelial phenotype. When cocultured with CSMCs, CECs formed capillary-like structures, and based on the extent of this capillary-like network, it was determined that a ratio of 1:4 in cell number between CECs and CSMCs was better than ratios of 1:1 and 1:9. It was also found that direct contact between CECs and CSMCs was necessary and a coculture period of 3 weeks was optimal. Autologous CSMCs were better than allogeneic CSMCs, and fibroblasts were completely incompetent. When treated with high glucose (25 mM), the CEC-CSMC coculture expressed significantly lower level of CD31 but significantly higher level of collagen-IV (Col-IV), and the diameter of the capillaries increased significantly, when compared with normal glucose (5 mM)-treated cocultures. These data are consistent with previously observed changes in the cavernous tissues of diabetic patients and thus suggest that the coculture system could be utilized for diabetic ED research.