T he open pit mining method is generally done by forming the slopes with aheight, width and angle have been determined to produce a design mining. Inorder to make sure the slope remained stable and can maintain coal productiontarget contained in the PT Muara Alam Sejahtera achieved geothecnical analysisis needed on Pit Alam 1 – 3 in order to determine the potential failure on theslopes. This study analyzed the slopes overall (highwall) using Equilibrium LimitMethod “Bishop simplified” through a probability of failure approach SimulationMonte - Carlo based on data of physical properties (unit weight) and mechanicalproperties (cohesion and angle of friction) rock intact and mass rock. Data fromthe geotechnical drilling is used as input parameters in the analysis of intact rockslope stability. While the value of cohesion and friction angle of the rock mass isobtained from field measurements of the discontinuous (scanline method) usingthe equation Generalised Hoek–Brown (2002). The results of this study comparedthe Safety Factor (FK) and Probability kelongsoran (PK) intact rock and rockmasses in accordance with Acceptable Criteria (Wesseloo and Read, 2010) wherethe overall slopes value of Factor of Safety (FOS) with low avalanche impactmore than 1.3 with Probability of Failure (POF) values less than 15% wereanalyzed using Slide 6.0 software. From the design of the existing pit PT MASanalyzed value of Factor of Safety (FOS) intact rock obtained for 2.4 and the rockmass have Factor of Safety (FOS) 1.3 with the percentage of Probability ofFailure (POS) 0%, meaning that the design meets the predefined criteria. While onthe final pit design value of Factor of Safety (FOS) intact rock obtained for 1.6and the rock mass have Factor of Safety (FOS) 1.3 with the percentage ofProbability of Failure (POS) 0%. Then in the sensitivity analysis, the parametersof the most dominant effect on the value of Factor of Safety (FOS) is angle offriction in the claystone material.