This study investigates the properties of protons in the magnetotail plasma sheet of Mercury. By superposing 5-year measurements from the MESSENGER spacecraft, we obtain the average energy spectrum of protons in the plasma sheet, which can be fitted nicely by the Gaussian-Kappa model. The proton density, pressure, and energy spectral index κ are found to be higher on the dawnside than on the duskside. The proton temperature shows a clearly outward radial gradient. The field-aligned density profile indicates that the protons in the outer plasma sheet move adiabatically. The pitch angle distribution reveals the reflected fluxes to be always less than the incident fluxes and indicates the loss of protons due to their impact on the planetary surface.