The proof of structural safety for historic masonry buildings and the evaluation of their bearing capacity according to current codes leads often to underestimation of their actual existing strength. In order to avoid this underestimation a new masonry strength formulation is needed, in which more influential parameters can be considered. Therefore, because concentrically loaded masonry is an abstract form, it is necessary to investigate the structural behaviour of masonry under eccentric loading. FEM-Analysis can help to understand the structural behaviour qualitatively. The experimental investigations are the base to build a theoretical model of structural behaviour and to formulate the bearing capacity of eccentrically loaded historical masonry. The comparison between the theoretically expected failure stress and the test results show an acceptable validity of the new approach. The suggested reduction factor is only valid for eccentricities with bending oui-of-plane and for one-unit masonry.