Sensitive detection of alpha fetoprotein (AFP) in serum is an important prerequisite to prompt definitive treatment decisions for reducing mortality rate of hepatocellular carcinoma. In this study, a label-free amperometric immunosensor was developed to detect AFP sensitively. It was based on platinum nanodendrites loaded on poly(diallyldimethylammonium chloride) functionalized molybdenum disulfide nanosheet hybridized polypyrrole nanotubes (Pt NDs/PDDA/MoSAPPy NTs). The Pt NDs and MoS2 nanosheet improved the catalytic activity, PPy NTs and PDDA increased electron transfer and enhanced the stability. The Pt NDs/PDDA/MoS2@ PPy NTs nanocomposite also had large active surface area and immobilized antibodies effectively. Therefore, the nanocomposite showed high catalytic activity, enhancing the electron transfer and immobilizing antibodies effectively, which amplified the current signal. Based on above advantages, the immunosensor had low detection limit of 17 fg mL(-1), wide linear concentration range from 50 fg mL(-1) to 50 ng mL(-1) for AFP (signal-to-noise ratio of 3), good reproducibility, selectivity and stability. The good analysis results of human serum samples implied that the immunosensor had bright potential application in clinical monitoring biomarkers.