The influence of the substrate temperature (T-s) on the microstructure and electron-induced secondary electron emission (SEE) properties of MgO/Au composite film prepared by reactive magnetron sputtering was investigated in order to improve the SEE performance of this composite film. During the deposition of MgO/Au film, a relatively high T-s is conducive to the growth of MgO grains and causes the formation of some large aggregated gold particles on which MgO grains cover in the composite film. In terms of the SEE properties of MgO/Au film, the increase of T-s brings about a significant improvement of SEE coefficient (8), while it also leads to a slightly accelerated SEE degradation under the continuous electron bombardment due to a faster surface charging. The MgO/Au film prepared at T, of 773 K has a delta value of 4.9 at a primary electron energy of 200 eV and the maximum delta value of 11.5.