This method for determining a mechanical property of a layered soft material, includes steps of a) generating an ultrasound wave (W1) focused towards a first point (P1) of the material, said wave, upon interacting with a layer of said material, generating in turn a Lamb (L1) wave propagating into said layer of the material, b) measuring, at a second point (P2) of the material belonging to said layer, a physical parameter of the generated Lamb wave, c) automatically determining the mechanical property of the layered soft material, based on the measured physical parameter. Step a) is performed by exciting a first ultrasonic transducer (401) with a first excitation signal (S401) during at most 50 ms, step b) is performed by exciting a second ultrasonic transducer (402) with a second excitation signal (S402) during at most 0.5 ms, to generate multiple excitation ultrasound waves (W2) focused towards said second point (P2) and, then, collecting multiple reflected waves (W2′) emitted in response, said first and second ultrasonic transducers each comprises an oscillator having a quality factor equal to or superior to 100, preferably equal or superior to 1000.