This paper shows impact of mutual coupling between circuits on accuracy of transmission line fault location using field data. Both one- and two-terminal test results are shown. Two-terminal test shows the test results with simulated and field data. Meanwhile, in case of one-terminal, the test emphasizes on showing test results with field data. The improved accuracy has been verified by comparing to those obtained from the standard algorithms. These tests were accomplished by using ATP-EMTP and applications which are developed on MATLAB.