Ravi Padma Sree and Manickam Chidambaram (2005) have evaluated the robustness of the system with PID controller of order (n = 5) by Kharitonov's theorem. In this note, it is pointed out that for low-order systems (n S 6), the robustness of the systems call be guaranteed by checking very simple frequency domain conditions based oil Hermite-Biehler theorem (Argoun. 1990). So, there is no need to formulate all the four Kharitonov's polynomials and also no need to calculate their roots. Thus, the computations call be reduced for such class of systems.