en High Voltage Engineering High Voltage Engineering Research Paper Research Paper This paper aims to measure and analyze of the leakage current of 20 kV polymer and porcelain metal oxide surge arresters under humid ambient conditions by applying different voltages to the arresters terminal. The characteristics of the leakage currents at that stage have been investigated when changes in the ambient humidity were introduced in an artificial fog chamber. It is assumed that magnitude of the noise level during the tests is constant. The frequency and resistive component peak efficient analysis can then be done on the leakage current signal. The idea behind this is to get indicators for investigating of surge arrester behavior in humid conditions. Two important indicators were obtained to evaluate the behavior of the surge arrester in humid conditions FFT Amplitude,Humidity,Leakage Current,Metal Oxide Surge Arrester, 79 86 http://ijeee.iust.ac.ir/browse.php?a_code=A-10-789-3&slc_lang=en&sid=1 K. Mokhtari k.mokhtari@stu.nit.ac.ir 180031947532846003244 180031947532846003244 No Department of Electrical and Computer Engineering, Babol University of Technology, Babol, Iran. M. Mirzaie mirzaie@nit.ac.ir 180031947532846003245 180031947532846003245 Yes Department of Electrical and Computer Engineering, Babol University of Technology, Babol, Iran. M. Shahabi shahabi.m@nit.ac.ir 180031947532846003246 180031947532846003246 No Department of Electrical and Computer Engineering, Babol University of Technology, Babol, Iran.