The invention provides a rack server which is suitable to be mounted in a server rack. The rack server comprises a case, a fan module and two ear frames. The case is provided with a bottom plate, two side walls, a first end and a second end, wherein the first end and the second end are opposite to each other. The two side walls are connected to the bottom plate, and each side wall is provided with a first fixing part at the first end and a second fixing part at the second end. The fan module is provided with an air inlet end and an air outlet end. The fan module is detachably arranged in the case in the way that the air outlet end of the fan module selectively faces the first end or the second end. The two ear frames are selectively mounted on the two first fixing parts or the two second fixing parts. When the two ear frames are mounted on the two first fixing parts, the case is suitable to be mounted in the server rack from the second end and the fan module is arranged in the way that the air outlet end faces the second end. When the two ear frames are mounted on the two second fixing parts, the case is suitable to be mounted in the server rack from the first end and the fan module is arranged in the way that the air outlet end faces the first end.