Reactive power dispatch (RPD) is one of the important tasks in the operation and control of power system. This paper presents a Differential Evolution (DE) - based approach for solving optimal reactive power dispatch including voltage stability limit in power systems. The monitoring methodology for voltage stability is based on the L-index of load buses. The objective is to minimize the real power loss subjected to limits on generator real and reactive power outputs, bus voltages, transformer taps and shunt power control devices such as SVCs. The proposed algorithm has been applied to IEEE 30-bus system to find the optimal reactive power control variables while keeping the system under safe voltage stability limit and is found to be effective for this task. The optimal reactive power allocation results obtained using DE are compared with other methods. It is shown that the objective function value is less than those of other methods.