A self-tuning regulator that uses a smaller sampling interval and a larger control interval resulting in periodically constant control, is described. Development of the mathematical model is given and a pseudo-state analysis technique, that can be used to analyse the plants where control and sample intervals are different, is introduced. A comparison of the proposed regulator with the conventional single sampling and control interval self-tuning regulator shows that the regulator with periodically constant control improves the system response.