The van der Waals force between dielectric plates comprising ultrathin conducting films was calculated by employing two models. In the first model, the ultrathin dielectric film was modeled as a dielectric plate of a small thickness, and the Lifshitz theory was applied. In the second model, an ultrathin dielectric film was modeled as a plasma sheet, which is an infinitesimally thin fluid carrying mass and charge. For each model, the interacting force was considered to be a function of the separation gap between the films, and the difference in the force-distance relationships of two was discussed. (C) 2017 Elsevier B.V. All rights reserved.