A system for extracorporeal photoimmunotherapy of biological fluid, constituted of blood or fractions thereof, comprising an instrument and a disposable assembly, the instrument comprising at least one set of UVA lamps suitable for photoradiation, a radiation chamber for the insertion and disposition in the chamber of a radiation container containing the fluid to undergo treatment, cooling elements for the radiation chamber and a pump element, the disposable assembly comprising a plurality of containers (4, 14) and pipelines (2, 5, 9, 22) for the containment and vehiculisation of the biological fluid, among which is a first pipeline, which on one side is for connection to an haematic cells container for containing haematic cells, the assembly also comprising the radiation container and an accumulation container for the intermediary storage of the blood or fractions thereof which is connected to the other side of said first pipeline; the instrument further compring the following elements: (a) at least one couple of electromagnetic-type clamps, there being inserted, inside each of the clamps, sections of dedicated pipe (7, 11) present in the disposable assembly, the couple of electromagnetic clamps being suitable for managing liquids to undergo treatment by means of the alternate opening and closure of the containers (4, 14) and pipelines (2, 5, 9, 22) in the disposable assembly; (b) at least one optical-type haematocrit reader sensor; (c) at least two pressure sensors suitable to identify overpressure inside the plurality of containers (4,14)and pipelines (2, 5, 9,22) in the disposable assembly; (d) at least two liquid presence sensors suitable to detect leaks of the liquid from the plurality of containers (4, 14) and pipelines (2, 5, 9,22) in the disposable assembly; (e) an RFID proximity reader suitable for reading and storing product identification data for each disposable assembly, (f) an arrangement for the transmission of data to a remote server; and the disposable assembly further comprising (g) a second pipeline connecting said accumulation container in the form of a recirculation container to said radiation container, and along which is positioned one of said sections of dedicated pipe; (h) a third pipeline connected to the second pipeline and for connection to a saline solution container for containing a saline solution, along which third pipeline one of said sections of dedicated pipe is positioned; and (i) an incubation container connected to said recirculation container by means of a further pipeline onto which are positioned two clamp elements. (a) at least one couple of electromagnetic-type clamps, there being inserted, inside each of the clamps, sections of dedicated pipe (7, 11) present in the disposable assembly, the couple of electromagnetic clamps being suitable for managing liquids to undergo treatment by means of the alternate opening and closure of the containers (4, 14) and pipelines (2, 5, 9, 22) in the disposable assembly; (b) at least one optical-type haematocrit reader sensor; (c) at least two pressure sensors suitable to identify overpressure inside the plurality of containers (4,14)and pipelines (2, 5, 9,22) in the disposable assembly; (d) at least two liquid presence sensors suitable to detect leaks of the liquid from the plurality of containers (4, 14) and pipelines (2, 5, 9,22) in the disposable assembly; (e) an RFID proximity reader suitable for reading and storing product identification data for each disposable assembly, (f) an arrangement for the transmission of data to a remote server; and the disposable assembly further comprising (g) a second pipeline connecting said accumulation container in the form of a recirculation container to said radiation container, and along which is positioned one of said sections of dedicated pipe; (h) a third pipeline connected to the second pipeline and for connection to a saline solution container for containing a saline solution, along which third pipeline one of said sections of dedicated pipe is positioned; and (i) an incubation container connected to said recirculation container by means of a further pipeline onto which are positioned two clamp elements.