The informative property of a data set is a necessary condition to ensure system’s identifiability. This paper studies the informative property of a data set in a single-input single-output (SISO) closed-loop system with a switching controller. We prove that this data set is informative as long as the controller switches among at least two modes (I.e., feedback laws). Our result does not require any assumption on the way of switching and removes the constraints on the switching manner required in some classical literature. Finally, the effectiveness of the result is validated through simulation case studies.