Abstract: Aiming at a class of uncertain descriptor systems with norm bounded perturbations in state variables, the problem of observer-based robust passive control is discussed. Using the methods of Lyapunov function and the magnified inequalities, the conditions for the closed-loop system to be generalized quadratically stability and robust strictly passive are given in the form of matrix inequalities. Then, the sufficient conditions for the existence of designed observer are presented in terms of linear matrix inequality (LMI), and the parameters of the observer-based controller are provided with the algorithm to solve the problem given. A numerical example is given to illustrate the effectiveness of the proposed method. The conclusions can be extended to the cases that there are perturbations in both the state and input.