The difficulties in designing an effective water level controller for the nuclear steam generator arise from highly nonlinear and nonminimum-phase plant characteristics as well as nonnegative input constraint. In this paper, a modified sliding mode controller with gain scheduling is proposed for nuclear steam generator water level control. A conventional proportional-integral with feed-forward controller is also developed, and the performance of two controllers is compared in the low power range. The modified sliding mode controller shows improvements in the overshoot, undershoot, and settling time.