An atomizer of a fuel electro-injector is equipped with a nozzle and a valve needle having a head, which is coupled to a sealing seat of the nozzle, and stem, which engages an inner seat of the nozzle; the stem and the nozzle define an annular passageway with a chamber that axially terminates at the sealing seat; the stem has an intermediate portion coupled in an axially sliding manner in the inner seat and defining a plurality of channels, the outlets of which are arranged on the annular chamber; the sealing seat and the head of the valve needle define a discharge section, which is annular and has a width that increases as the opening stroke of the valve needle proceeds; the ratio between the depth and the outer chord of the minimum cross-section of the channels is greater than or equal to two.