Rock mass classification systems are the most commonly used empirical tools in preliminary design of rock slopes. In spite of numerous advantages, these systems lack the common drawbacks of classification systems originated from uncertainties. These drawbacks may lead to similar or so close quality scores for different rock mass properties. Fuzzy Sets is a rising trend in describing Geomechanical problems by including the expert opinion. Especially in the case of weak rocks it allows prediction of more realistic rock mass quality scores. Although the empirical systems form a basis for the preliminary slope stability investigation, slope height and overall slope angle are still two missing important characteristic slope parameters. However, there have been some attempts to describe the graphical presentation of rock quality score, slope height and overall slope angle relation. These charts are called as slope performance charts. This chapter presents a short review on integration of Fuzzy RMR with these charts to provide a useful modification for the case of weak rock slopes.