The invention provides an ultrafiltration membrane assembly and an ultrapure water manufacturing method using the same. The ultrafiltration membrane assembly can obviously reduce the concentration oftrace ions in ultrapure water, in particular, warm ultrapure water. The ultrafiltration membrane assembly (10) comprises a plurality of hollow fiber membranes (1) and a cylindrical shell (2) for storing the plurality of hollow fiber membranes (1). A first nozzle (2a) and a second nozzle (2b) are arranged on the periphery of the cylindrical shell (2) along the axial direction of the cylindrical shell (2), and are separated from each other; and processed water is introduced into and concentrated water is discharged out through the first nozzle (2a) and second nozzle (2b). A third nozzle (6a) anda fourth nozzle (6b) are arranged on two ends of the cylindrical shell; and water, which has penetrated the hollow fiber membranes (1), and discharged water flow out through the third nozzle (6a) andthe fourth nozzle (6b). A pair of fixing parts (3a)(3b) fixes the plurality of hollow fiber membranes in a prescribed configuration and seals the cylindrical shell (2).