Given the high costs of investment for transmission network development and the key role of transmission networks in restructured space, using FACTS devices is crucial. In this paper, the optimal Placement of FACTS in transmission networks is investigated. The numerical studies section has solved the problem in different sections with three different types of FACTS devices. Numerical studies of the problem have been solved for a 118-bus network related to the western part of the American power grid. The comparison of the results shows that the simultaneous use of different types of FACTS devices can perform better. Also, the use of series and parallel FACTS devices can work in a complementary way and create better compensation. The results of the studies on the 118-bus network show that FACTS devices work locally, and in large networks, a larger number of FACTS devices should be used for compensation and significant impact. Of course, considering the issues related to investment and other restrictions, it is not possible to use this equipment in practice. This shows the importance of optimal placement of FACTS devices.