To determine the role of allogeneil graft of mesenchymal stem cells in mammalian longevity, mesenchymal stem cells were isolated from BALB/c mouse uterine-incision delivery fetus by two successive density gradient centrifugations, and then were purified and amplified by adherent culture. Identified P1 mesenchymal stem cells were injected (i.v.) through vena caudalis into the 15-month-old female BALB/c mice three times. The mice were evaluated with ultrasoundcardiogram, autopsy, score of cardiac, skin, lung, kidney, colon histopathology and serum total superoxide dismutase activity, maleic dialdehyde content, glutathione peroxidase activity. The results showed that after transplantation, the long-term surviving stem cells were found to be located in many organ tissues with in situ Y chromosomal hybridization dyeing. Median life span was increased in these animals after transplantation. Skin, cardiac, lung, kidney and colon pathology development were delayed. The retrogradation of heart function was attenuated, the increase of heart mass index (the mass of heart/the mass of the body), and serum maleic dialdehyde content, the decrease of spleen mass index (the mass of spleen/the mass of the body), serum total superoxide dismutase activity and glutathione peroxidase activity were reduced three months after transplantation (all P<0.05). These results support the idea that longevity can be enhanced by transplantation of mesenchymal stem cells and reinforce the hypothesis of mesenchymal stem cell as antiager.