The paper presents a coherency-based identifying method of the optimum site for power-system stabilisers. After decomposing a multimachine power system into several coherent groups, the most effective selection of a generator to be equipped with a stabiliser in each coherent group is determined. The coherency recognition is made by using a coherency index in the frequency domain. Through the numerical analysis indicated in the paper, a simple and effective method for determining the best locations of stabilisers is proposed