M esenchymal stem cells (MSCs) are multipotent adult stem cells that can beisolated from umbilical cord blood (UCB). Until now, the anti-cancer effect ofMSCs still remains controversial between scientists. Some evidences demonstratethat MSCs can induce apoptosis of cancer cells. However, there are also studiesthat show MSCs may favor tumor growth. Based on this unclear effect of MSCson tumors, this study is therefore initiated to investigate the anti-cancer effect ofsecretome contained in UCB-MSCs conditioned medium (CM) on cervical cancercell line HeLa in vitro. Hela cells were treated with UCB-MSCs CM in variousconcentrations (0.2%, 2%, and 20%) for 24 or 48 hours. The count of dead HeLacells was evaluated by cell viability analysis using trypan blue. The transition ofmitochondrial transmembrane potential (TMP) which occurs during apoptosis wasassayed by ΔΨM analysis using DiOC6 with flow cytometer. Cell viabilityanalysis showed that death of HeLa cell was induced by UCB-MSCs CM, and anincrease in concentrations and treatment time concomitantly resulted in increasednumber of dead HeLa cells. Treatment of HeLa cells with UCB-MSCs CM 0.2%for 24 hours was sufficient to induce death of HeLa cells. ΔΨM analysis showedthe decrease of TMP, indicating an increase in mitochondrial membranepermeability of HeLa cells These results demonstrated that secretome contained inUCB-MSCs CM had the ability to induce HeLa cell apoptosis via mitochondrialpathway.