A backlight module having replaceable lamp module is provided. The backlight module includes a replaceable lamp module, a light-guiding plate, a frame and a positioning and protecting mechanism. The light-guiding plate is disposed over the bottom surface among four sides of the frame, wherein one side of the light-guiding plate and a corresponding side of the frame form a sliding groove. The replaceable lamp module is set in the sliding groove and slidably along the sliding groove. The positioning and protecting mechanism comprises a protecting device set on the replaceable lamp module and a positioning device set on the frame. The protecting device is capable of forming a gap between the replaceable lamp module and the bottom of the sliding groove in order to protect the replaceable lamp module from scraped by the structures of the backlight module while the replaceable lamp module is inserting into the sliding groove. The protecting device and the positioning device are capable of positioning and holding the replaceable lamp module in the sliding groove while the replaceable lamp module reaches the predetermined position in the backlight module, and meantime the gap is disappeared.