Voltage stability issues have attracted the interest of power system researchers worldwide. It is important to maintain the system stability, or else it would lead to voltage collapse and consequently complete blackout of the system. In this paper the voltage stability indices, Fast Voltage Stability Index (FVSI) and Voltage Reactive Power Index (VQI Line ) are used to determine the stability of a system. These indices are used to identify the most critical line and bus of the system. Under single line outage condition, effect of placing a TCSC in the system on FVSI & VQI Line has been observed. An IEEE 6 bus system has been considered for simulation purpose.