This paper considers a robust observer-based H_∞ controller design method for singular systems with parameter uncertainties using an LMI condition. The sufficient condition for the existence of controller and the controller design method are presented by a perfect LMI condition in terms of all variables using singular value decomposition, Schur complement, and change of variables. Therefore, one of the main advantages is that a robust observer-based H_∞ controller can be established by solving one LMI condition compared with existing results. Numerical example is given to illustrate the effectiveness of the proposed controller design method.