Abstract: This study presented a novel quantum-inspired binary gravitational search algorithm method for solving the optimal power quality monitor placement problem in power systems for voltage sag assessment. In this algorithm, the standard binary gravitational search algorithm is modified by applying the concept and principles of quantum behaviour as to improve the search capability with faster convergence rate. The optimization considers multi objective functions and handles observability constraint determined by the concept of the topological monitor reach area. The overall objective function consists of three functions which are based on the number of required monitor, monitor overlapping index and sag severity index. The proposed algorithm is applied on the radial 69-bus distribution system and the IEEE 118-bus transmission system. To show the effectiveness of the proposed algorithm, its performance is compared to the other optimization techniques, namely, binary gravitational search algorithm and binary particle swarm optimization and quantum-inspired binary particle swarm optimization.