An assembly structure for a data storage device of a server includes a tray (60), a frame (100), and a transverse movement member (200). The tray (60) has a guiding pillar (10). The frame (100) is disposed on the tray (60). The frame (100) includes a side wall (110) and a hook plate (112) disposed on a surface of the side plate (110). The transverse movement member (200) is connected to the hook plate (112) of the side plate (110) and is movable transversely. The transverse movement member (200) includes a guiding slot (220) movable with respect to the guiding pillar (10) and includes a restriction recess (230) restricting the hook plate (112) from moving transversely. Accordingly, this simple structure can achieve handy operation, and allows quick assembly and disassembly of the data storage device without the use of any tool.