The focus of this talk is to discuss the influence of a gradient in hardness and Young’s modulus in ultrafine-grained laminated metal composites on the cyclic mechanical properties. The ultrafine-grained composites are produced by the accumulative roll bonding process. For the optimization of such laminated structures, a fundamental understanding of the microstructural interactions and deformation processes at the internal material interfaces is necessary. Special attention is put on aluminum/steel composites, as in these composites a high gradient in hardness and Young’s modulus is present at the layer interfaces. The mechanical properties are measured in dynamic three-point bending tests, conducted on a vibraphone testing machine at higher frequencies. By scanning electron microscopy, the influence of the meso- and microstructure on the fatigue properties is intensively studied. Furthermore, internal stresses during elastic straining are calculated using finite element simulations. In the aluminum/steel composites the fatigue properties are drastically increased compared to aluminum mono-material sheets, as well as to composites based on two different aluminum alloys, where only a hardness gradient at the material interface exists. This increase is related to two different reasons: Due to the higher stiffness of the steel layers, a stress redistribution to the inner steel layers takes place reducing the stress in the outer aluminum layer. This is also proven by FE-simulations. Therefore, macro-crack initiation is strongly suppressed in these aluminum/steel composites enhancing the high cycle fatigue life. At higher stress amplitudes, pronounced crack deviation at the aluminum steel layer interface occurs leading to a strongly enhanced low cycle fatigue life.