When two small drops or bubbles approach one another, a dimpled liquid film is formed between them. A model is developed for the dynamics of a drainage film in which the interfacial mobility is recognized. It shows that the tangential mobility of interfaces plays an important role in film drainage. An expression for predicting the coalescence time, required for the thinning and rupture of a liquid film, is represented as a function of the radii of bubbles or drops and the physical properties of the fluids and inter faces. The predicted result is in good agreement with previous experimental results.