Recently, concerns over voltage instability phenomena have been increasing, because significant voltage drops are regarded crucial in stable operations. Thus, effective voltage control schemes using voltage stability indices have been brought to attention in a considerable number of studies. The conventional voltage stability indices are mainly based on evaluating voltage stability margins to a critical point. The operator usually determines proper voltage range in power systems. In this paper we propose a voltage stability index VMPI (voltage margin proximity index) considering voltage limits, especially lower voltage limits. Simulations are run using the IEEJ West 30 machine 115 bus system