One of the main challenge of the future in the utility sector is constructing the new transmission line corridor. This is due to the fact that land compensation cost related to a new transmission line corridor expansion becomes very expensive. In addition to that, the high carbon emission related to the additional conventional energy based power generation to meet dramatically increased electricity demand and the volatility nature of the existing transmission networks are some of the main drivers to implement FACTS controller in transmission network for flexible, reliable, efficient and stable power transmission. In this paper a comprehensive modeling of STATCOM and UPFC FACTS controllers for improving the transmission line capacity and voltage profile of the power system are studied. The two FACTS controllers are modeled for an IEEE 5-bus power system separately using Newton Raphson load flow algorithm in PSAT to investigate their impacts on power flow (transmission line capacity and voltage profile) result. As a result of the power flow studies performed with and without FACTS controller, it was observed that the FACTS controllers increased the capacity of the existing transmission line, improving the voltage profile of the system and highly affects the power flow of the IEEE 5-bus power system network.