A fixing bracket for a slide rail of an open rack includes a fixed cover, a sliding cover and plural fasteners. Both fixed and sliding covers cover the exterior of the slide rail, and the sliding cover can slide appropriately with limitation, and a pair of the slide rails are installed symmetrically on both sides of a chassis, and the fixing bracket is provided for fixing the chassis onto an open rack which is a rectangular enclosed frame structure similar to a door frame, and the fixed cover and the sliding cover have a first fixing plate and a second fixing plate configured to be corresponsive to the open rack. With a sliding design of the sliding cover, the fasteners can be used to fix the chassis onto the two opposite sides of the rack by adjusting the width of the open rack.