The robustness of continuous-time generalized state-space systems with unidirectional perturbations is investigated in this paper. By transforming the original problem to a robust rank problem, we provide a simple method to compute the exact bounds on such perturbations so that the important features of regularity, impulse immunity, and stability of nominal systems are all presented. This approach can be viewed as a generalization of Fu and Barmish’s result to generalized state-space setups. It also provides a tractable solution to many practical robustness problems. This is clearly explained by a simple circuit example.