Background/Aims: We invented a cell-mixed sheet consisting of autologous fibroblast cells and peripheral blood mononuclear cells (PBMNCs) to treat refractory cutaneous ulcers. These sheets secrete the growth factors needed throughout the wound healing process in animal models. Methods: We performed this study as a pilot phase I clinical trial (UMIN-CTR: UMIN000031645). Fibroblast cells were isolated and cultured from the oral tissue, and PBMNCs were collected by apheresis. A cell-mixed sheet was prepared by co-culturing these collected cells for 3 days. The primary observation index was safety, including all adverse events. Additional observation indices were wound healing over 1, 3, and 6 months; wound healing rate at 7 days and 1, 3, and 6 months. Results: Six patients with venous leg ulcers (VLUs) were enrolled in the study, including three patients who were treated with the cell-mixed sheet transplantation. One patient was excluded because no fibroblast cells grew from the oral tissue culture, and other two were excluded because the growth factor secreted from mixed-cell sheets did not reach the reference value. The VLUs of two patients who received the cell-mixed sheet transplantation healed, and the VLU in one patient decreased in size. Conclusions: This pilot study demonstrated that cell-mixed sheets might be a new topical intervention to treat VLUs. However, it was also suggested that this treatment might be limited when using autologous cells collected from patients with VLUs. Therefore, it may be necessary to use high-quality allogeneic cells instead of autologous cells to improve the feasibility of this treatment.