Secondary electron emission (SEE) plays a crucial role in the gain performance of devices, such as electron multipliers and microchannel plates (MCPs). Gain performance could be improved by increasing the secondary electron yield (SEY) of device surface. Al2O3 coating is an ideal material for SEE, benefiting from its high SEY. The Al2O3 coating deposited on inner device walls by atomic layer deposition (ALD) can improve the gain performance of devices. In this study, the SEE characteristics of Al2O3 coatings were investigated experimentally. A series of Al2O3 coatings with thicknesses of 1-30 nm were prepared on Si substrate through the ALD method. Then, the SEY of the coatings were quantified as a function of primary electron energy in the range of 100∼1500 eV. Furthermore, an equation describing the true SEY as a function of thickness was established by applying theory of Dionne's SEE model. This work presents potential approach for controlling the SEE level of Al2O3 coatings through thickness adjustment and is crucial for comprehending the SEE of composite materials. © 2019 Author(s).