A device for crystallizing a molecule to be crystallized which comprises: - at least one crystallization cell, the crystallization cell comprising: • a crystallization chamber, in which is arranged a cavity intended to receive a first solution S1 containing the molecule to be crystallized and its crystal seeds, and optionally at least one buffer, the cavity including an optical base and an opening, • a dialysis membrane, • a tank intended to be fitted onto the crystallization chamber, so as to create a watertight compartment formed on the one hand by the tank and on the other hand by the crystallization chamber, the compartment being intended to be filled with a second solution S2, called crystallization solution which contains components selected from the group composed of the crystallization agents, the additives and the buffers, - at least one image acquisition means, - at least one addition means arranged to add in the tank components selected from the group composed of the crystallization agents, the additives and the buffers to the solution S2 and/or - at least one sampling means arranged to sample in the tank all or part of the solution S2, said crystallization device is characterized in that the opening faces the optical base and in that the dialysis membrane is intended to cover the opening of the cavity of the crystallization chamber. - at least one crystallization cell, the crystallization cell comprising: • a crystallization chamber, in which is arranged a cavity intended to receive a first solution S1 containing the molecule to be crystallized and its crystal seeds, and optionally at least one buffer, the cavity including an optical base and an opening, • a dialysis membrane, • a tank intended to be fitted onto the crystallization chamber, so as to create a watertight compartment formed on the one hand by the tank and on the other hand by the crystallization chamber, the compartment being intended to be filled with a second solution S2, called crystallization solution which contains components selected from the group composed of the crystallization agents, the additives and the buffers, • a crystallization chamber, in which is arranged a cavity intended to receive a first solution S1 containing the molecule to be crystallized and its crystal seeds, and optionally at least one buffer, the cavity including an optical base and an opening, • a dialysis membrane, • a tank intended to be fitted onto the crystallization chamber, so as to create a watertight compartment formed on the one hand by the tank and on the other hand by the crystallization chamber, the compartment being intended to be filled with a second solution S2, called crystallization solution which contains components selected from the group composed of the crystallization agents, the additives and the buffers, - at least one image acquisition means, - at least one addition means arranged to add in the tank components selected from the group composed of the crystallization agents, the additives and the buffers to the solution S2 and/or - at least one sampling means arranged to sample in the tank all or part of the solution S2, said crystallization device is characterized in that the opening faces the optical base and in that the dialysis membrane is intended to cover the opening of the cavity of the crystallization chamber.