This work analyses entropy generation in composite walls which lose heat with both convection and radiation, simultaneously. Temperature-dependent thermal conductivities and internal heat generations are assumed for both materials. The nonlinear system of differential equations is solved with the differential transformation method (DTM) which is a semi-analytical technique. The temperature and entropy generation data derived from the DTM are validated against analytical solution for convective composite walls with temperature-independent thermal conductivities and internal heat generations. In the view of the fact that composite walls are one of the classical examples in many scientific communities, the local and total entropy generations presented in this study can be useful addition for many scientific and engineering fields where one wants to minimize the irreversibility of the system.