A backlight module and an engagement fitting thereof, and a display device using the backlight module are provided. The backlight module includes: a rear shell including a back plate and a side plate formed with an assembly hole; a middle frame engaged with the side plate and formed with an engagement portion extending toward the assembly hole; and an engagement fitting disposed in a receiving space and adjacent to the side plate. The engagement fitting includes a buckling member and an engagement member penetrating through the assembly hole, the buckling member is for buckling with an optical component set, the engagement member is for engaging with the engagement portion, and thereby achieving tight engagement of the rear shell, the middle frame and the optical component set. The present invention can effectively simplify the structure of the backlight module, improve the structural strength and reduce the production cost.