A filter unit for blood and blood derivatives comprises a body (1) defined by two injection-moulded half-shells (2, 3) of thermoplastic polymer material, there being present between said half-shells (2, 3) a cavity (4) containing a filtering element (5) having two opposing flat faces (5A, 5B), an inlet opening (9) and an outlet opening (13) made on the opposing outer surfaces (2K, 3K) of said body (1) communicating with said cavity (4). Each of said half- shells (2, 3) comprises a projecting perimetral flange (30), the flanges (30) of the overlapping half-shells being welded together to form a flange (40) of the body of the filter unit and connect the two half-shells (2, 3) together, the filtering element (5) being wholly contained within the cavity (4) of such body (1) and pressed by shelves (55) projecting into such cavity (4) from each half-shell (2, 3) in the vicinity of its perimetral border (70) and on the two opposing faces (5A, 5B), said shelves (55) retaining said filtering element (5) in a stable position within cavity (4), said thermoplastic polymer material being yielding and semi-rigid.
