We report an electrochemical non-enzymatic method for hydrogen peroxide (H2O2) detection based on Ag nanoparticle-decorated MoSe2 (Ag/MoSe2-500) hybrid nanostructures. These hybrid nanocomposites are easily prepared by in situ reduction of Ag+ on the surface of MoSe2. Benefiting from the strong synergy of Ag nanoparticles and MoSe2 nanosheets in enhancing electrical conductivity, the Ag/MoSe2-500 hybrid nanostructures perform excellent sensing activity for H2O2 electrocatalytic reduction with a wide linear range of 0.02-15.2 mM, a high sensitivity of 400.0 μA mM-1 cm-2 and a low detection limit of 0.39 μM (S/N = 3). Furthermore, the sensor displays satisfactory reproducibility and stability and is applicable for practical quantitative analysis of H2O2 in milk and orange juice samples. In a word, Ag/MoSe2-500 nanocomposites are promising candidates for non-enzymatic H2O2 sensing in the fields of biology and food science.