A backlight unit, a display device, and a method for manufacturing a backlight unit are provided. The backlight unit includes a light guide plate including a main body and a first protrusion portion protruding from a side of the main body; a plastic frame provided at a periphery of the side of the light guide plate, wherein a side of the plastic frame proximal to the light guide plate has an engaging groove provided thereat, and the first protrusion portion of the light guide plate protrudes towards the plastic frame and is engaged in the engaging groove; and a light shielding structure provided on a light exit surface of the first protrusion portion, wherein an orthographic projection of the light shielding structure on the light exit surface of the first protrusion portion partially covers the light exit surface of the first protrusion portion.