Abstract Background aims A previous study demonstrated that human umbilical cord blood–derived mesenchymal stromal cells (hUCB-MSCs) have superior wound-healing activity compared with fibroblasts in vitro . However, wound healing in vivo is a complex process that involves multiple factors. The purpose of this study was to compare the effects of hUCB-MSCs and fibroblasts on diabetic wound healing in vivo . This study especially focused on collagen synthesis and angiogenesis, which are considered to be the important factors affecting diabetic wound healing. Methods Porous polyethylene discs were loaded with either fibroblasts or hUCB-MSCs, and a third group, which served as a control, was not loaded with cells. The discs were then implanted in the back of diabetic mice. During the first and the second week after implantation, the discs were harvested, and collagen level and microvascular density were compared. Results In terms of collagen synthesis, the hUCB-MSC group showed the highest collagen level (117.7 ± 8.9 ng/mL), followed by the fibroblast group (83.2 ± 5.2 ng/mL) and the no-cell group (60.0 ± 4.7 ng/mL) in the second week after implantation. In terms of angiogenesis, the microvascular density in the hUCB-MSC group was 56.8 ± 16.4, which was much higher than that in the fibroblast group (14.3 ± 4.0) and the no-cell group (5.7 ± 2.1) in the second week after implantation. Conclusions These results demonstrate that hUCB-MSCs are superior to fibroblasts in terms of their effect on diabetic wound healing in vivo.