The paper considers the influence of core saturation on the dynamics of magnetostrictive fast-acting actuator. The field-circuit mathematical model of the dynamic operation of the capacitor-actuator system is applied. Two kinds of magnetostrictive core nonlinearity are taken into account. It has been proved that the saturation of the B-H curve practically does not affect the current, and capacitor voltage waveforms, but significantly affects a core elongation waveform. The computed results are compared with experimental ones.