The paper presents a rule-based variable-gain power system stabiliser (PSS) for power systems, which has been implemented in the laboratory by transputers for real-time control tests. This stabiliser has been developed from the conventional PSS, but with a variable gain, which is adjusted on-line to meet the damping requirement of power systems. The real-time adjustment of the stabiliser gain is based on two control rules by detecting the oscillation status in the systems. The object of this arrangement is to achieve a stabiliser which is robust to the changes of the operating conditions of power systems and can suppress the oscillation detected in the system more effectively and with less detrimental influence on the transient performance of power systems. Results of laboratory tests are presented in the paper to show the effectiveness of this rule-based variable-gain power system stabiliser.