A polyamide/polyurethane composite filament yarn, which filament comprises a polyamide sheath component and a polyurethane eccentric core component exposed with a neck portion of uniform width on the surface of the filament, is manufactured by a process comprising inserting, immediately before extruding from a spinneret orifice, a molten polyurethane flow obliquely from upwards and incorporating said polyurethane flow eccentrically into a molten polyamide flow flowing down in said conduit, while a small part of said polyurethane flow radially projected in a restricted width penetrating through the thinnest portion of said polyamide flow flows down along the inner wall of said conduit. For this process, an employable spinneret comprises a leading duct for polyamide connecting to an orifice via a vertical conduit, another leading duct for polyurethane connecting to an injection pipe obliquely extending therefrom, protruding into said conduit, opening immediately before said orifice and having a slit extending longitudinally at the under side along the entire protruded length.