Rock slope stability analysis with the use of analytical and numerical approaches is usually a complicated engineering task because of complex behaviour of the rock mass and also of the various affecting parameters. On the other hand, even though the wide application of empirical methods, they don’t have an acceptable accuracy and efficiency in all situations due to the consideration of the specified influencing major factors. The Rock Engineering Systems (RES) is a systems approach which can be considered as a suitable method for rock engineering analyses and classifications particularly in areas with complex environment and multiple affecting parameters. In this method, the interactions between the system’s parameters are analyzed and then the effect of each parameter on the subject (system) is considered. The aim of this paper is to utilize the RES approach to classification of rock slopes in Khosh-Yeylagh mountainous road between Shahrood and Azadshahr cities in Iran. In this way, the study region and its conditions have been visited and some stations on the rock slopes have been selected. Then, the key steps of the mentioned approach such as selection of the most important parameters generating the instability, establishment of the interaction matrix and its coding, setting up the classification menus, defining the instability index in the form of a mathematical formula have been consecutively followed. Then, the experimental data of rock and rock joint physical characteristics were achieved and the indices for each slope were calculated. In this manner, the rock slopes in the stations were classified from the instability point of view. Finally, as a preliminary validation on the utilization of systems approach in the study region, the stability of investigated rock slopes were analyzed using an empirical method and the results were compared. The comparisons showed a rather good coincidence between the given classes of two methods. The results of this research showed that the utilization of the systems approach could be considered very useful in rock slope stability analysis specifically in large scale problems with various affecting parameters.