Summary: This paper investigates the problem of non-fragile observer-based passive control for descriptor systems with time-delay. The perturbations in both control gain and observer gain of the observer-based controller are considered. For the cases of the additive perturbations and multiplicative perturbations, sufficient conditions are given such that the closed-loop systems are admissible and passive with dissipation $η$. The observer-based controller gains are obtained from the solutions of linear matrix inequalities. Moreover, the maximum dissipation of the system is provided. Simulation examples are given to show the effectiveness of the design methods.