A method was developed for determining the surface tension coefficient at the interface of two immiscible liquids or of a gas and a liquid. Basic in this method is the measurement of the capillary rise of a droplet of one of the phases placed on the surface of the other phase. It is shown that the capillary rise is a function of the surface energy of the droplet and the viscous friction of the phases. A mathematical model of the dynamics of a liquid droplet is supported by experiments.