Objective To investigate the supernatant of umbilical cord-derived mesenchymal stem cells (UCMSCs) on tumor necrosis factor-α(TNF-α) and apoptosis protein caspase-3 in diabetic rats model with skin ulcer. Methods 45 Sprague-Dawley rats were randomly divided into control group (acute wounds group), phosphate buffered saline (PBS) group and UCMSCs supernatant group. The diabetic rat model was constructed by injecting with alloxan by tail vein and feeding with high-fat diet. Diabetic skin ulcer (DSU) rat model was constructed by scratching a wound and infusing suspension of Staphylococcus aureus. In the control group, the diabetic rats (n=15) were scratched to form a wound and treated by tail vein injection of 100μl PBS. In the PBS group, DSU rats (n=15) were treated by tail vein injection of 100μl PBS, and then 100μl PBS was dropped at the ulcer site. In the UCMSCs supernatant group, freeze-dried powder of UCMSCs supernatant was dissolved in 200μl PBS, 100μl of which was injected into the tail vein of DSU rats (n=15), and other 100μl was dropped at the ulcer site. After 5 days of the treatments, the levels of serum TNF-αwere detected by radioimmunoassay method, and the expression of TNF-αand caspase-3 in the ulcer tissues of rats was detected by polymerase chain reaction and Western Blot. Results The levels of TNF-αin the PBS group [(35.9±3.7)μg/L] were significantly higher than that of the control group [(11.4±4.9)μg/L] and the UCMSCs group [(14.7±6.6)μg/L] (all P<0.05). The levels of mRNA and protein expression of TNF-αand caspase-3 in the UCMSCs group were significantly lower than those of the PBS group (all P<0.05), and have no significant differences with respect to those of the control group (all P>0.05). Conclusions UCMSCs supernatant treatments can effectively down-regulate the expression of TNF-αand caspase-3 in ulcer tissue of DSU rats, and play an anti-inflammatory and anti-apoptotic effect.