Tumor microenvironment turn-on nanoprobes that could specifically detect the occurrence of diseases possess great potential in early diagnosis. Here, a GSH activated nanoprobe was designed for fluorescence and 19 F magnetic resonance (MR) dualmodal turn-on imaging of tumors. Specifically, fluorescence AgInS 2 quantum dots (QDs for fluorescence imaging) were coencapsulated with perfluoro-15-crown-5-ether (P 19 FCE for 19 F MRI) by amphiphilic polymers and further coated with in situ formed manganese dioxide (MnO 2 ) nanoshells, which served as efficient fluorescence and 19 F MR quenchers due to energy transfer and paramagnetic relaxation effects, respectively. The overexpressed GSH in tumors would decompose the MnO 2 nanoshells, resulting in remarkable enhancement of both fluorescence and 19 F MRI signals of the nanoprobes, accordingly lighting up the tumor site.