A fastening module for fastening a data storage device is provided. The data storage device includes first and second positioning apertures. A frame of the fastening module includes a retaining hole, and first and second positioning holes. The data storage device is slidably received in the frame. A securing member of the fastening module includes a main body, a pivot member, and a pin. The main body includes a pivot hole pivotally connected by the pivot member. A securing piece of the pivot member passes through the retaining hole and rotates relative to the main body to fasten the securing member to the frame. When the securing piece passes through the retaining hole, the pin passes through either the first or second positioning hole and inserts into either the first or second positioning aperture to fasten the data storage device at different positions.