The mining panel “Revier VI” of the Magnesite Mine Breitenau is located at a depth of around 900 m below surface and is mined using sublevel stoping with backfill. The aim of this thesis is the quantification of the mechanical rock mass properties using different rock mass classification systems as well as in-situ and laboratory tests. The results of the conducted investigations show that the overall rock mass strength exceeds the stress level which has been determined by numerical simulation based on topography for the mining panel “Revier VI”. In order to assess the rock mass conditions, the essential fundamentals of rock mass properties that contribute to the overall rock mass strength are described in a first step. The shear strength of discontinuities, the grade of disturbance and the rock strength determine the strength of rock mass. Rock strength can be determined by simple tests, while the other two factors can only be estimated using classification systems. Rock mass classification systems of different authors were then used for the quantification of the mechanical rock mass properties. Due to the inhomogeneity of the rock mass, it was divided into sections and then the rock mass was geotechnically assessed section by section. In addition, core drilling was performed to gather mechanical strength properties of the rock material as another input parameter for the rock mass classification. The rock mass strength was then estimated using approaches of different authors. A two-dimensional stress-analysis of the mountain-slope was carried out to simulate the primary stress acting on the orebody. The degree of the local variety of rock strength and grade of disturbance leads to inaccuracy concerning the results. Hence the geotechnical parameters were substituted by a large amount of discretely distributed random numbers, in respect to their real distribution. A method similar to the Monte-Carlo-analyses was then carried out to calculate the rock mass strength. The results of this analysis were compared with a simple tool for rock mass evaluation, the “Rock Condition Factor”, which supports of the conducted investigations. The rock mass strength averages 33 % of the mean rock strength.