Cancer is one of the major life-threatening diseases among human beings. Developing a simple, cost-effective and biocompatible approach to treat cancers using ultra-low doses of light is a grand challenge in clinical cancer treatments. In this study, we report for the first time that nano-sized graphene oxide (GO) exhibits single-photon excitation wavelength dependent photoluminescence in the visible and short near-infrared (NIR) region, suitable for in vivo multi-color fluorescence imaging. We also demonstrate in both in vitro and in vivo experiments to show that nano GO can sensitize the formation of singlet oxygen to exert combined nanomaterial-mediated photodynamic therapeutic (NmPDT) and photothermal therapy (NmPTT) effects on the destruction of B16F0 melanoma tumors in mice using ultra-low doses (~0.36 W/cm2) of NIR (980 nm) light. The average half-life span of the mice treated by the GO-PEG-folate-mediated NmPDT effects is beyond 30 days, which is ~1.8 times longer than the mice treated with doxorubicin (17 days). Overall, the current study points out a successful example of using GO-PEG-folate nanocomposite as a theranostic nanomedicine to exert simultaneously in vivo fluorescent imaging as well as combined NmPDT and NmPTT effects for clinical cancer treatments. © 2016 Elsevier Ltd.