Catalytic nanomedicine with high oxygen-generation efficiency may find applications in alleviating tumor hypoxia and improving the efficiency of photodynamic therapy (PDT). In this study, a catalytic nanosystem (Ce6-Rh@MPDA) was developed using mesoporous polydopamine nanoparticles (MPDA) to encapsulate catalase-like rhodium nanoparticles (Rh NPs) and photosensitizer chlorine6 (Ce6) for photoacoustic/fluorescence dual imaging-guided tumor therapy. The Rh NPs can catalyze the production of O2 from tumor-enriched H2O2in situ, in which the mesoporous structure of MPDA plays an important role via improving the catalytic efficiency of Rh NPs. Moreover, the hyperthermia generated by both MPDA and Rh NPs under laser irradiation accelerates the O2 generation to promote the PDT. The Ce6-Rh@MPDA nanoparticles described herein represent a multifunctional metal-based catalytic nanomedicine which not only alleviates tumor hypoxia but also enables a synergistic antitumor treatment using PTT and PDT.