Fast Fourier transform(FFT) technique in time domain was applied in the measurement of the anti-permeability of organic coating on metal.In this technique,the frequency range is in the very low frequency region(from 10 Hz to 0.1 Hz).It can be done without expensive lock-in amplifier or frequency response analyzer with the result that the measurement is fast and reliable.The results are in good agreement with those measured at high frequency region by lookin amplifier.