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 λ_ex/λ_em 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.