速率控制步骤，又称为限速步骤，简称速控步，也译作决速步（rate-determining step (RDS)），是一个化学词汇，用以表达在化学反应中，反应速率最慢的一个步骤。认识一个化学反应当中最慢的一个步骤的重要性在于能够有效率地改善整个化学反应的速度，从而达致更高的产率等。一个常用的比喻就是一条狭窄的水管——无论水流有多快，也无法改变水的流量。速率控制步骤就是影响整个化学反应速率的那条水管。

In chemical kinetics, the overall rate of a reaction is often approximately determined by the slowest step, known as the rate determining step (RDS) or rate-limiting step. For a given reaction mechanism, the prediction of the corresponding rate equation (for comparison with the experimental rate law) is often simplified by using this approximation of the rate determining step.