T The presence of cracks on the slopes of hills Limestone relatively widening anddeep, is worried to cause a potential landslide that will make a fatality anddestruction to infrastructure in Limestone Hills in Kaliwadas, Karangsambung,Kebumen, Central Java. This research was conducted to determine the effect ofvariations in the physical and mechanical properties of the rock slope stabilit yaround the crack. A number of rock samples taken from the research location, andtested the physical and mechanical properties. Laboratory tests on rock samplesinclude physical properties, uniaxial compressive strength test, and Direct ShearStrength Test. Furthermore, the calculation of the value of SF (Safety Factor) andPA (Probability Avalanche) using limit equilibrium method "Janbu Simplified" andMonte Carlo sampling method assuming a kind of plane avalanche.Based on Uniaxial Compressive Strength (UCS) test conducted and ISRM (1979)Classification of Intact Rock Strength, Calcarenite Limestone can be categorized asLow Strength, Top and Bottom Calcilutite Limestone categorized as Very Low.Based on Direct Shear Strength Test, peak and residual Cohesion value ofCalcarenite Limestone is 0.31 Mpa and 55.6 kPa; peak and residual of Internalfriction angle is 43.44° and 34.8°. For Top Calcilutite Limestone, peak and residualCohesion value is 0.22 Mpa and 36.36 kPa; peak and residual of Internal frictionangle is 39.83° and 31.2°. Lastly, for Bottom Calcilutite Limestone, peak andresidual Cohesion value is 0.23 Mpa and 34.28 kPa; peak and residual of Internalfriction angle is 42.44° and 29.8°Based on Slope Stability Analysis, probabilistic Safety Factor and LandslideProbability of cross-section C – D is 2.06 and 0%, cross-section E – F is 1.84 and0.2% as well as cross-section G – H is 3.17 and 0%. According to the official Orderby the Ministry of Public Works (KepMen PU. No378/KPTS/1987), the SafetyFactor of natural slope must be >1.5. This shows the slope in the vicinity of thecrack is relatively stable with Safety Factor > 1.5.A sensitivity analysis done between rock mass properties and slope stability showsa negative correlation between Weight and Safety Factor. This is due to the fact thatincreased weight will cause increased ratio between “driving” force to “resistingforce”, causing Safety Factor to fall. On the other hand, the same study shows apositive correlation between Cohesion/ Internal Angle of Friction and SafetyFactor. The bigger the Cohesion and Internal Angle of Friction are, the more“resisting” force the slope will have; this causes decreased ratio of “driving” forceto “resisting” force and thus, Safety Factor will increase.