Stability parameters are very important in the analysis and design of reinforced concrete cantilever retaining wall structures. One of the parameters to increase the stability of this retaining wall is to add a shear key structure. Shear keys can increase wall stability, resist shear, increase stiffness, resist lateral loads, and increase load capacity. The purpose of this research is to determine the level of stability (overturning and shearing) of reinforced concrete cantilever retaining walls by varying the shear key dimensions with the same cross-sectional area. The method used is a quantitative method using data on the properties of soil materials, reinforced concrete, and the geometry of retaining wall structures. The analysis uses the help of Geo5 software, which is geotechnical software for solving problems in the geotechnical field. In this research, four models of reinforced concrete cantilever retaining walls have been created, including model 1 (b/h = 0), namely the model without a shear key, model 2 (b/h = 1), namely square shear key, model 3 ( b/h = 1/4) is a vertical rectangular shear key and model 4 (b/h = 4/1) is a horizontal rectangular shear key. The results of the analysis produce rolling stability with an increase in rolling moment and a decrease in moment of resistance on average of 8.32% and 4.43% respectively for the model without a shear key with a maximum rolling safe factor in the horizontal rectangular shear key model of 2.24. Likewise, the shear stability of the model with a shear key results in an increase in ground shear force and a decrease in active shear force on average of 11.76% and 105.93% respectively compared to the model without a shear key with a maximum shear safe factor in the horizontal rectangular shear key model of 3.96.