In recent decades, H2O2 has been promoted as a health indicator because its moderate to high levels can cause some health problems. Herein, we developed a new fluorescent nanoprobe for rapid, selective and sensitive detection of H2O2. The fluorescent nanoprobe is composed of fluorescein dye (FLS) as a fluorescent probe and MnO2 nanosheets (MnO2 NS) as a quencher. In this study, H2O2 can reduce MnO2 NS in the synthesized composite and release FLS, causing sufficient recovery of fluorescent signal related to the concentration of H2O2. The nanoprobe, with λex/λem at 495/515 nm, has a linear range of 0.04–30 μM, with a limit of detection (LOD) of 7.5 nM and a limit of quantitation (LOQ) of 21 nM. The mean relative standard deviation (RSD) was 2.6% and the applicability of the method was demonstrated by the determination of H2O2 in water and cosmetic samples.