A single neuron controller including flexible AC transmission systems (FACTS) devices in power system is introduced. SVC and TCSC are plugged into the network as additional modules for small perturbation studies. The single neuron model is employed to form the composite model for improving the electro-mechanical mode of power system under probabilistic condition, and genetic algorithm is used to optimize the parameter of the proposed controller. Under selected SVC and TCSC parameters, the probabilistic eigenvalues with and without FACTS device and the single neuron controller are compared on an eight-machine testing system. The effectiveness of the proposed method is investigated.