Tower footing resistance and fault current division factor are important design factors for evaluation of the lightning performance of the transmission line and/or design of the grounding electrode system. The periodic measurement of those factors are also important to verify that the grounding performance of the towers has been maintained good. However, the direct measurement of those factors in operating or energized condition is very difficult because of many practical reasons, such as the difficulty of disconnecting overhead groundwires from the tower under test. With supports by GECOL (General Electricitiy Company of Libya), we had a special chance to conduct Fall-Of-Potential (FOP) test on the energized 220 kV transmission towers before and after disconnecting the overhead groundwires from the towers under test. In this paper, the FOP test results on the towers and the fault current division factors estimated from the comparision of the FOP tests with and without overhead groundwires were presented. The computer models for the FOP test simulations were also constructed to find that the simulated results agreed very well with the measured ones.