Abstract: In this paper robust reduced-order observer-based H-infinity controller design for uncertain descriptor systems is investigated. Firstly, based on strict linear matrix inequalities, a suffcient condition for H-infinity control of uncertain descriptor systems is proposed to design the state feedback H-infinity control law. Then the control gain is used to design the reduced-order observer. Based on an explicit general solution to a class of generalized Sylvester equations, a parameterized design method is presented with the constraint of H-infinity performance.