Although human embryonic stem cell (hESC) hold therapeutic potential, teratoma formation has deterred clinical translation. Manganese (Mn2+) enters metabolically active cells through voltage-gated calcium channels and subsequently, induces T1 shortening. We hypothesized that serial manganese-enhanced MRI would have theranostic effect to assess hESC survival, teratoma formation, and hESC-derived teratoma reduction through intracellular accumulation of Mn2+. Firefly luciferase transduced hESCs (hESC-Lucs) were transplanted into severe combined immunodeficient mouse hindlimbs to form teratoma. The chemotherapy group was injected with MnCl2 intraperitoneally three times a week. The control group was given MnCl2 only prior to manganese-enhanced MRI. Longitudinal evaluation by manganese-enhanced MRI and bioluminescence imaging was performed. The chemotherapy group showed significant reduction in the teratoma volume and luciferase activity at weeks 6 and 8. Histology revealed increased proportion of dead cells and caspase 3 positive cells in the chemotherapy group. Systemic administration of MnCl2 enabled simultaneous monitoring and elimination of hESC-derived teratoma cells by higher intracellular accumulation of Mn2+. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.