Fe 3 O 4 /PPy/Ag nanocomposites with core/shell/shell structure were prepared and used for fabricating nonenzymatic H 2 O 2 sensor. The nanocomposites were prepared with a three-step process, and proved by characterizations such as transmission electron microscopic, X-ray diffraction and X-ray photoelectron spectroscopy. The electrochemical investigation revealed that the composites had excellent catalytic property toward H 2 O 2 . The sensor could detect H 2 O 2 with a wide linear range from 5μM to 11.5mM, and a low detection limit of 1.7μM. Additionally, the sensor exhibited long-term stability, good reproducibility and anti-interference.