In order to study the effect of the frequency and the intensity of low-frequency alternating-current (AC) electric fields on lean combustion, the effects of 100/80/60/40 Hz AC electric fields on premixed CH4/N-2/O-2 flames with excess air ratio of 1.2/1.4/1.6 have been investigated in a constant volume combustion bomb. The results show that the frequency and the applied voltage of low-frequency fields have significant effects on lean combustion. Firstly, the mean flame propagation speed decreases with the electric field frequency, and meanwhile, the combustion peak pressure decreases and the peak time increases. Secondly, both the mean flame propagation speed and the combustion peak pressure increase linearly with the applied voltage, while the peak time decreases. What's more, the developing degree of the ionic wind effect decreases with the electric field frequency and increases with the applied voltage, which can be used to explain the experimental results. The low-frequency AC electric fields can enhance the lean combustion effectively, which has a positive meaning in the further study of the electric field assisted combustion theory. (C) 2016 Elsevier Ltd. All rights reserved.