A thin soft elasto-plastic interphase between two different media is under consideration. The intermediate layer is assumed to be of infinitesimal thickness and is modeled by nonlinear transmission conditions which incorporate the elasto-plastic material behavior of the layer. The case of pressure-independent (von Mises) as well as pressure-dependent yield condition is theoretically treated. Finite element analysis of a bimaterial structure with such an imperfect elasto-plastic interface (von Mises) shows the efficiency of the approach and illustrates some restrictions of its application.