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It is of great importance to develop well-designed tumor-targeting theranostic nanoplatform based on the nanomaterials with good stability in physiological environment.The aim of this study was to construct a stimuli-responsive drug-releasing and diagnostic-imaging nanoplatform for cancer theranostics.First, the MnO2 nanosheets with a size of 20-60 nm were synthesized and modified with (3-Aminopropyl) trimethoxysilane (APTMS), and then ftmctionalized by NH2-PEG2000-COOH (PEG).Second, folic acid (FA) was conjugated with the PEGylated MnO2 nanosheets for get a tumor targeting system.Last,doxorubicin (DOX), was loaded onto the modified nanosheets through a physical adsorption.This multifunctional nanoplafform with good biocompatibility can efficiently deliver DOX to tumor cells in vitro and in vivo, leading to enhanced anti-tumor efficiency.Furthermore, it also can respond to slightly acidic environment and high concentration of reduced glutathione (GSH), which caused degradation of MnO2 into manganese ions enabling magnetic resonance imaging (MRI).The longitudinal relaxation rate r1 was 2.26 mM-1 s-1 at pH 5.0 containing 2mM GSH.These reduction and pH dual-responsive biodegradable nanosheets combing efficient MRI and chemotherapy paved a way for tumor-targeting theranostic application.