A method for measuring the nonlinear coefficients of piezoceramic resonators with low signal excitation is presented. It consists of the intermodulation produced by two signals with variable amplitude and closely spaced in frequency at the neighborhood of the resonance, performing the measurement of the intermodulation distortion signals at frequencies near excitation. This method is highly sensitive and allows nonlinear measurements to be taken at relatively low levels, avoiding thermal effects. The module and argument of the nonlinear increase in the impedance can be determined by the analysis of these measurements. This method is compared with other previously used methods, and the advantages of the proposed method are analyzed. The described nonlinear coefficient allows us to understand and foresee the nonlinear behavior near the resonance: amplitude-frequency shift effect, decrease of mechanical quality factorQ,and the jump phenomenon observed in frequency sweeps. ©1997 American Institute of Physics.