In the diploma, a parametric analysis of seismic resistance of a stone masonry building in Čezsoča was performed. The first part presents an overview of the testing methods being the basis for redesign of existing buildings since they define the depth of knowledge of the construction. The emphasis is on non-destructive testing, which is preferred due to its characteristics and continuous development in technology, presenting a quickly developing and promising area. Next, we described the process of assessment of seismic resistance of existing masonry buildings in accordance with contemporary standards. Different mechanisms of shear failure for unreinforced masonry walls are explained. The simplified N2 method is presented step by step. In the practical part of the thesis, the analyzed building and the results of in-situ testing are presented. The parametrical analysis was carried out using two programs (Sremb and 3Muri) for non-linear seismic analysis of masonry structures. We defined the seismic resistance in dependence of the parameter of knowledge of the construction, the choice of an appropriate failure mechanism, consideration of safety factors and strengthening the building with grout technique. The results of the analysis show that the requirements of contemporary standards can be fulfilled by systematic grouting. Due to different suppositions for the behaviour of the building under seismic loading, the results of seismic resistance achieved using the two programs differ significantly. The differences appear also due to the presumed failure mechanism. Investment in preliminary in-situ testing is valuable since it is possible to come much closer to the available seismic resistance while considering the actual material characteristics.