The knowledge of viscosity, which determines the flow of material under applied stresses, is important for many processes of the material production. Data on viscosity of thin amorphous films are necessary for development of molding technology, which allows fast fabrication of various components for integrated optics. Chalcogenide films attract great attention due to their non-linear optical properties and possibility of viscosity variation by light illumination. Despite of importance of data on the film viscosity, no methods of their direct measurements were reported. We propose such method and apply it for measurements of viscosity of As₂₀Se₈₀ chalcogenide films in a temperature range 378–403 K. We have obtained that coefficients of viscosity vary in the range 3 × 10⁷–10¹⁰ Pa·s, with the activation energy 2.9 eV. The thin film viscosity coefficients are 2–5 times smaller compared to those for massive glasses.