In this paper, the authors aim at designing digital control system for ITU (Istanbul Technical University) TRIGA Mark-Ii reactor A self-tuning control algorithm with the generalised minimum variance strategy is employed. The control system is based on a second order linear model with unknown but time varying parameters. Genetic algorithm is applied hers to the problem of estimating controller parameters. The control rod speed is selected as a control variable. The controller controls the reactor power to follow the given trajectory. Self-Tuning control is achieved by an iteration at each sample interval through the following cycle; parameter estimation. calculation of trajectory, calculation of control signal.