Abstract: A chair backrest includes a support frame having an inner periphery provided with a support portion which has an upper edge provided with a plurality of locking blocks, and a backrest cushion having a periphery provided with an elastic snapping portion which is snapped onto the support portion of the support frame and retained by the locking blocks of the support frame. Thus, the backrest cushion is mounted on and detached from the support frame by forcing and retracting the snapping portion of the backrest cushion, so that the chair backrest is assembled and disassembled easily and quickly without needing aid of any hand tool, thereby facilitating the user assembling and disassembling the chair backrest, and thereby facilitating the user replacing the backrest cushion.