Power system state estimation with exclusive utilization of synchronous phasor measurements demands that the system should be completely observable through PMUs only. To have minimum number of PMUs, the PMU placement issue in any network is an optimization problem. In this paper, a model for the optimal placement of phasor measurement units (PMUs) in electric power networks is presented. Optimal measurement set is determined to achieve full network observability during normal conditions, i.e. no PMU failure or transmission line outage is considered. Observability analysis is carried out using topological observability rules. A connectivity matrix modification based integer linear programming is used as an optimization tool to obtain the minimal number of PMUs and their corresponding locations while satisfying associated constraint. Simulation results for IEEE 30-bus and New England 39-bus test systems are presented and compared with the existing techniques, to justify the effectiveness of proposed method. In All investigations, the zeroinjected buses are considered to obtain the best answers.Keywords-Phasor measurment unit; integer linear programming; network observability; optimal placement; network connectivity.I.