Properties of low-frequency noise in the amorphous InZnO thin film transistors have been investigated in this paper. Due to the emission and trapping processes of carriers between trapping states located in the interface between the IZO layer and gate insulator, the drain current spectral density shows a 1/fγ(γ =0.75) low-frequency noise behavior. In addition, the normalized drain current spectral density is decreased linearly with the increase of gate length and width. This property confirms that the low-frequency noise in the IZO TFTs is due to the flicker noise in the channel, the contribution of source/drain contact and parasitic resistances can be ignored. Finally, based on the number fluctuation theory and the mobility fluctuation theory, the γ and average Hooge's parameters have been extracted to estimate the quality of devices and materials.