The resonance spectrums of disc type piezoceramic resonators with different electrode sizes were measured in the frequency range from 100 kHz to 1 MHz. Besides the fundamental mode, some overtone and other vibration modes existed in this frequency range, depending on the electrode size. The series resonance frequency of fundamental modes of the resonators increased with the reduction of the electrode size. When the electrode size was decreased down to 80% of size, some small spurious signals will exist; these spurious signals may be caused by another vibration mode such as twist mode or bending mode. The planar electromechanical coupling factor increased first with the decreasing of the electrode size, and reached a maximum when the diameter of electrode was decreased down to 80% of size, and then decreased with the decreasing of the electrode size.