Barrier film coating is the most appropriate and widely used approach to protect solid dosages from moisture, particularly for water-sensitive drugs including herbal medicines. This study aims to produce the barrier film of a typical herbal medicine by applying an electrostatic deposition process with ultrafine powders of hydroxypropyl cellulose so as to achieve the functionality of moisture protection. The flowability of the ultrafine powders was significantly improved by adding suitable nano additives. The applied plasticizer in the coating formulation had a significant effect on the water vapor permeability of the film. Also, the electrostatic deposition efficiency were significantly affected by the charging voltage of the electrostatic gun and the plasticizer ratio. Curing time and temperature were identified as two critical parameters for barrier coating in terms of surface morphology and hygroscopicity. All the results suggested that the electrostatic deposition process is capable to produce efficient barrier film for herbal medicines. (C) 2020 Elsevier B.V. All rights reserved.