In this paper, depth positioning of a spherical URV which utilizes variable ballast as actuator is presented. Since the model of this system is nonlinear therefore feedback linearization is utilized in this depth positioning. The idea of feedback linearization is to algebraically transform nonlinear systems dynamics into (fully or partly) linear ones, so that linear control techniques can be applied. This method can stabilize the equilibrium point of this system which is unstable in open loop system. From the control analysis and simulation results, it can be observed that the asymptotical stabilization is achieved by tracking the error. Hence, feedback linearization can also be applied for tracking a trajectory of desired depth position. © 2008 IEEE.