Based on 2D Janbu's generalized procedure of slices (GPS), a new three-dimensional slope stability analysis method has been developed, in which all forces acting on the discretized blocks in static equilibrium are taken into account in all three directions. In this method, the potential sliding mass is divided into rigid blocks and each block is analyzed separately by using both geometric relations and static equilibrium formulations. By introducing force boundary conditions, the stability problem is determined statically. The proposed method can be applied to analyze the stability of slopes with various types of potential sliding surfaces, complicated geological boundaries and stratifications, water pressure, and earthquake loading. This method can also be helpful in determining individual factor of safety and local potential sliding direction for each block. As an extension of 2D Janbu's method, the present method has both the advantages and disadvantages of Janbu's generalized procedure of slices.