An expert system is developed to assist in the decision-making of the reactive power/voltage control problem. The knowledge required to perform the task is identified. To alleviate a voltage problem, empirical rules are used to generate appropriate control actions when slight voltage violations occur. Controls such as shunt capacitors, transformer tap changers and generator voltages are utilized. Theoretical justification of the empirical rules is presented. When it is judged that the voltage problem is so severe that empirical judgements may not be reliable, the developed expert system can help in formulating the problem so that an available application software package can be effectively utilized. In this paper, production rules are proposed to perform the above functions. Numerical examples are also presented.