Abstract: The invention concerns a method for determining the vanishing temperature of petroleum product crystals, characterized in that it comprises the following steps: introducing the sample to be analyzed in a measuring cell (4), arranged in a cryostatic chamber (1); connecting a laser emitter (6) and an associated optical receiver (7) to pass an optical beam through the sample to be analyzed and recording the light intensity received by the receiver (7); gradually lowering the temperature of the cryostatic chamber (1) then increasing it again gradually while recording the curve representing the variations in the light intensity received by the receiver (7) based on the temperature; and determining the vanishing temperature of the crystals from said curve.