Objective The pharmacokinetics of cellular drugs were studied with the mouse umbilical cord mesenchymal stem cells ( mUCMSC) tracing method and mdx mice. Methods mUCMSC were labeled by GFP transfection, and a 0. 4 mL (5×10⁶ GFP-mUCMSC) cell suspension was injected locally into the abdominal cavity of mdx mice with damaged gastrocnemius and diaphragma. The fluorescence signal in the mice was observed with a live imaging system at five timepoints including 1 h, 3 h, 5 h, 24 h, and 1 wk post injection. The mice were euthanized and their diaphragms were collected to obtain frozen sections for fluorescence microscopy. Results mUCMSCs were successfully labeled when they were co-cultured with the viral vector at an MOI of 150 for 72 h. One hour after local intraperitoneal injection of the GFP-mUCMSCs, a strong green fluorescent signal was observed with the live imaging system under the injection position on the abdominal wall of the mdx mice, and the fluorescent area gradually decreased with time. After 24 h, the fluorescence intensity was obviously weakened, and the fluorescent area was greatly reduced. These fluorescent signals had almost disappeared after one week. At this time, the fluorescent signals could still be observed in the diaphragm of the mdx mice under the fluorescence microscope, and this signal was significantly higher than that of the control group without cell injection (P<0.05). Conclusions Umbilical cord mesenchymal stem cells injected into the abdominal cavity of the mdx mice entered the injured diaphragm and their GFP fluorescent signals gradually disappeared within 1 week. Thus, a live imaging system is an effective tool for monitoring the dynamic distribution and clearance rate of stem cells in vivo.