A facile one-pot synthetic route is reported to prepare algae-like molybdenum disulfide/polypyrrole (MoS2/PPy) nanocomposite through a redox reaction between ammonium tetrathiomolybdate and pyrrole monomer under a hydrothermal condition without any other templates. The as-prepared unique algae-like MoS2/PPy nanocomposites are composed of few layer MoS2 nanosheets, which are covered with PPy. Structural and morphological characterizations of this unique nanocomposite are investigated by Fourier-transform infrared spectra, Raman spectra, X-ray diffraction pattern, X-ray photoelectron spectra, energy-dispersive X-ray spectroscopy, and transmission electron microscopy. The as-prepared MoS2/PPy nanocomposites exhibit an excellent peroxidase-like catalytic activity toward the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2) in acetate buffer solution (pH 4.0), which provides a facile strategy for the colorimetric detection of H2O2 with a high sensitivity.