The invention relates to a device for crystallising a molecule to be crystallised, which comprises: at least one crystallisation cell (1) that includes a crystallisation chamber (2) for receiving a first solution S1 containing the molecule to be crystallised and the crystal seeds thereof, a dialysis membrane, and a container (7) to be filled with a second solution S2 that contains constituents selected from the group containing crystallisation agents, additives and buffers; and at least one image acquisition means. The crystallisation device (9) is characterised in that it includes: at least one addition means arranged to add, to the container (7), constituents selected from the group containing crystallisation agents, additives and buffers of solution S2; and/or at least one sampling means arranged to collect, from the container (7), all or a portion of solution S2. The invention also relates to a crystallisation method.