Janus nanoparticles (JNPs) have multiple configurations for molecular imaging, targeting, and therapeutic effects on cancers; these properties have made these particles attractive for biomedical applications. Nonetheless, smart strategies for the controlled synthesis in a liquid phase and exploration of the appropriate applications of JNPs remain a challenge. In this study, a unique liquid-phase method was applied to fabricate Mn3O4-TiO2/ZnO/Fe3O4 multifunctional binary transition metal oxide-based JNPs, using the concept of epitaxial growth and lattice mismatch among synthesized materials. Transmission electron microscopy and scanning transmission electron microscopy results revealed that the created materials are embedded in the form of dimers with good dispersion and homogeneous growth in a nonpolar solvent. Pluronic (R) F-127-coated Mn3O4-TiO2 JNPs were utilized as a contrast agent in T-1-weighted magnetic resonance imaging (MRI) and in photodynamic therapy (PDT) for cancers in vitro and in vivo. In vivo T-1-weighted MRI of the heart, liver, and kidneys in mice after intravenous injection of the nanoparticles revealed high sensitivity and biocompatibility of as-synthesized Mn3O4-TiO2 JNPs. Results of synchrotron X-ray fluorescence microscopy mapping showed the stability of the nanocomposites and efficiency of penetration into the cytoplasm and perinuclear area. Inorganic TiO2 photosensitizers showed promising tumor ablation performance in PDT in vitro and in vivo at low intensity of UV irradiation (5.6 mW.cm(-2)) because of their ultrasmall size and photodegradable stability. These results reveal that multifunctional Mn3O4-TiO2 JNPs enhance a T-1-weighted MRI contrast and have excellent properties for PDT and therefore, may be a novel agent for cancer theranostics.