The present invention provides a backlight module and a housing unit structure thereof. The backlight module includes a back plate having a first edge, a second edge, a third edge and a fourth edge. The edges of the back plate are provided with a housing including a plurality of housing unit structures. The housing unit structures have a strip shape or an L-shape, respectively, and are disposed on the back plate by connecting or spacing a distance to each others to assemble into a housing. The backlight module uses an adjustable modular design to adjust the number of the housing unit structures for being suitably applied to various backlight modules with different sizes. Except for reducing the use of material, the development cost and time of the backlight module can be saved.