Abstract： Objective To investigate the possibility of human umbilical cord blood mesenchymal stem cells' migrating to the gastric carcinoma xenografts. Methods Gastric cancer cells SGC-7901 were injected subcutaneously into one side of the inguinal groove in the hairless mice to establish the animal model.Gastric cancer-bearing mice were divided randomly into two groups and five in each group (n =5). Then mesenchymal stem cells and the fibroblast HFL-Ⅰ labeled with fluorescent dye SP-DiI were injected at the opposite side. Ten days later, the mice were put to death, and the gastric carcinoma xenografts, liver, spleen,lung and the tissue of injected point were obtained. Cryosections from frozen tissues were processed for fluorescent microscopy and the distribution of MSC and fibroblasts in different organs were observed. Adjacent sections were stained with HE. Results Human umbilical cord blood mesenchymal stem cells were mainly distributed in gastric carcinoma xenografts (0.0150±0.0079), but were found only a little in liver (0.0010±0.0005), spleen (0.0015±0.0012), lung (0.0014±0.0008) and injected point (0.0043±0.0039). Fibroblasts were mainly observed in the tissue of injected point, but none in other tissues (P ＜0.01). Conclusion Human umbilical cord blood mesenchymal stem cells have the tendency of migrating to tumor sites, suggesting that it can be hopefully used in the diagnosis and treatment of gastric cancer.