Low-energy electron diffraction on the K-adsorbed Ag(001) surface showed remarkably different pattern changes, when the K coverage dependence was observed in the different temperature ranges at 315–335 and 125–150 K. This different changes can be explained by the reconstruction of the substrate Ag(001) surface at higher temperatures and the K overlayer structure change at lower temperatures. Potassium coverage dependences of the work-function changes and electron energy loss spectra support the model of the missing-row type reconstruction at higher temperatures.