Cancer is one of the main causes of morbidity and mortality. Although a number of techniques are available for treatment, these methods still have a number of drawbacks, destroying healthy tissues and cells to cause various side effects. Here we present the synthesis and biological application of a composite nanomaterial, folic acid (FA)-conjugated graphene oxide (GO) nanosheets functionalized with manganese dioxide (MnO₂) nanoparticles. While FA-conjugated GO nanosheets can be used for targeted photothermal therapy (PTT) when irradiated with a near infrared (NIR) light, MnO₂ nanoparticles degrade hydrogen peroxide (H₂O₂) in the cancer microenvironment, countering hypoxia. Further the nanoparticles can be used as a contrast agent in MRI imaging. We demonstrated that MnO₂-FA-GO nanosheets were uptaken by HeLa cells overexpressing FA receptors to induce NIR irradiation-mediated hyperthermia (35% viability). Therefore, this composite MnO₂-FA-GO nanosheet could be a powerful carrier for cancer targeting and PTT applications.