The problem of output tracking control is considered for a general class of nonlinear differential-algebraic systems. Regularization algorithm proposed here provides sufficient conditions for the existence of a regularizing feedback controller that renders the closed-loop system to have an index one. Based on the regularization algorithm, another algorithm is developed for constructing a tracking controller, which guarantees that the outputs of the closed-loop system track the desired signals asymptotically. Simulation results on a typical chemical process show that the developed design method gives a satisfactory control performance.