[en] A composite film based on K₈P₂W₁₆V₂O₆₂·18H₂O decorated by Au–Pd nanoparticles was prepared by the layer-by-layer self-assembly method. This composite film exhibits enhanced electrocatalytic performance, repeatability and long-term stability for the simultaneous determination of dopamine and ascorbic acid at biological pH (pH 7.0). The proposed electrochemical sensing film for simultaneous detecting dopamine and ascorbic acid shows rather low detection limit of 8.3 × 10⁻⁷ and 4.3 × 10⁻⁷ M and a linear response range from 2.1 × 10⁻⁶ to 2.06 × 10⁻³ M and 1.2 × 10⁻⁶ to 1.61 × 10⁻³ M, as well as no interference from the common interfering species at an applied potential. -- Abstract: A novel composite film based on Dawson-type phosphovanadotungstate K₈P₂W₁₆V₂O₆₂·18H₂O (P₂W₁₆V₂) decorated by Au–Pd alloy nanoparticles (Au–Pd) was fabricated on quartz, silicon and ITO using the layer-by-layer self-assembly method. The composite film was characterized by UV–vis spectroscopy, X-ray photoelectron spectra, atomic force microscopy, Scanning electronic microscope, cyclic voltammetry and differential pulse voltammetry. The composite film can be employed for sensitive and simultaneous determination of dopamine and ascorbic acid at biological pH (pH 7.0). Linear analytical curves were obtained in the ranges from 2.1 × 10⁻⁶ to 2.06 × 10⁻³ M and 1.2 × 10⁻⁶ to 1.61 × 10⁻³ M for dopamine and ascorbic acid by DPV methods, respectively. The low detection limit for dopamine and ascorbic acid were 8.3 × 10⁻⁷ and 4.3 × 10⁻⁷ M, as well as no interference was observed from the common interfering species such as glucose, uric acid, L-cysteine, CH₃OH, CH₃CH₂OH and H₂O₂. The composite film was used for dopamine and ascorbic acid determinations in real samples with satisfactory results. With high sensitivity and selectivity, the proposed electrochemical sensor would provide a simple method for simultaneous determination of dopamine and ascorbic acid in practical applications