T The study was conducted in mining area phase 6 and phase 7 Batu Hijaupit with a total 40 observation points. This study aims to determine the causes oflandslides in the mining area phase 6 and phase 7 and to know the relationship andthe influence of the quality of rock mass on deformation. The study was conductedwith the window mapping method. In this study rock mass classification was carriedout using the Rock Mass Rating (RMR) method and a statistical test was performedbetween the value of RMR and the speed of deformation. The results of thecalculation of the deformation speed for the Poor rock class are with a speed rangeof 0.19-0.49 mm / day, Fair rock 0.17-0.51 mm / day and Good rock 0.04-0.18 mm/ day. The decline in speed range from Poor rock and rock Fair to Good rock provesthat the quality of rock mass has an influence on deformation events. The statisticaltest results, namely the exponential regression test, show that there is an influenceof rock mass quality on the deformation speed where each increase in the value ofone unit of RMR will decrease the deformation speed by 0.001 – 0,003 mm / day,correlation coefficient test with the value r = -0.675 proving that both variablecorrelates "strong" with the type of negative correlation and the significance testwith the results of hypothesis testing that "significant correlation" shows if there isa correlation and proves that the quality of the rock mass affects deformation