Photodynamic therapy (PDT) is commonly employed in clinics to treat the cancer, but because of the hypoxic tumor microenvironment prevalent inside tumors, PDT therapeutic efficiency is not adequate hence limiting the effectiveness of PDT. Therefore, we designed a nanocomposite consisting of reduced nanographene oxide (rGO) modified with polyethylene glycol (PEG), manganese dioxide (MnO2), upconversion nanoparticles (UCNPs), and Chlorin e6 (Ce6) to spark oxygen production from H2O2 with the aim of relieving the tumor hypoxic microenvironments. For in vivo tumor PDT and photothermal therapy (PTT), UCNPs-Ce6-labeled rGO-MnO2-PEG nanocomposites were used as a therapeutic agent, augmenting the therapeutic efficiency of PDT via redox progression through the catalytic H2O2 decomposition pathway and further achieving excellent tumor inhibition. It is important to mention that degradation of MnO, in an acidic cellular microenvironment leads to the creation of a massive volume of Mn2+ which was employed as a contrast mediator for magnetic resonance imaging (MRI). Our research postulates an approach to spark O-2 formation through an internal stimulus to augment the efficiency of MRI- and computerized tomography (CT)-imaging-guided PDT and PTT.