Electrical power system has become large and complicated, so it is subjected to sudden changes in load levels. Stability is an important concept which determines the stable operation of the power system.The modern trend is to employ by installing Flexible Alternating Current Transmission System (FACTS) devices in the system for effective utilization of transmission resources.The FACTS devices contribute to the power flow improvement besides, they extend their services in transient stability improvement as well, study and analyze the stability of the system through rotor angle and voltage .The object of this work is to improve the stability of the Iraqi National Super Grid System (INSGS) by using optimal FACTS devices in different optimal locations under fault conditions.Two test systems are studied, the first system is IEEE or WSCC (9-bus bars), and the second system is the Iraqi (400 KV) electrical network 24-bus bars.The load flow program was implemented using the Newton-Raphson method and the numerical solutions of non-linear differential equations are solved using Trapezoidal method.A comparison has been made between five types of FACTS (UPFC, SSSC, TCSC, SVC, STATCOM) at optimal location of the Iraqi grid and (9-bus bars) to get optimal FACTS devices by (voltage stability, rotor angle ).The results obtained showed that the installation of Unified Power Flow Controller (UPFC) is optimal devices for an improvement of the stability by damping the voltage and rotor angle oscillations.