AbstractGeological discontinuities play an important role in the evaluation of rock slope stability. Romana's Slope Mass Rating (SMR) system provides a methodology to quantify rock slope stability. Employing Bieniawski's Rock Mass Rating (RMR) to classify the rock mass of an investigated slope, SMR enables an objective determination of the rating adjustment values based on discontinuity orientation-slope orientation, respective dips angles and slope excavation methods. However the surface roughness of the discontinuities and their peak friction angles (αp) that are fundamental in determining rock slope stability are not directly considered in this evaluation. A more sustainable approach to rock slope stability assessment proposed here combines the SMR determination with the determination of the peak friction angle, αp of the discontinuity surfaces. Based on this proposal, the potential for slope failure can be quantified as follows: if SMR predicts failure and dip angle of the discontinuity (βi) > the peak friction angle (αp) the slope has a very high failure potential; if SMR predicts failure and βi αp, the slope has low failure potential and if stable according to SMR and βi < αp, the slope can be considered as stable.