An exemplary support assembly is provided for supporting an electronic device on a supporting surface. The support assembly includes a shell receiving the electronic device, and a back-support. The shell defines an elongated sliding rail. The back-support includes a prop stand, and a prop seat slidable in the sliding rail. One side of the prop stand is rotatably engaged in the prop seat and serves as a spindle. The other sides of the prop stand are thus movable between a folded position substantially coplanar with the prop seat and a supporting position angled relative to the prop seat. When the other sides of the prop stand are in the supporting position, a tilt angle of the electronic device on the supporting surface is adjustable by sliding the prop seat in the sliding rail.