A backrest for a chair, including a bag-like upholstery material, with which a back frame is upholstered by fitting the bag-like upholstery material onto the back frame that has a pair of right and left side frames extending in an up-down direction. A low-friction member is disposed on at least one of an inner surface of both side portions of the upholstery material and an outer surface of the right and left side frames contacting the inner surface of the side portions of the upholstery material, the low-friction member being configured to reduce a sliding resistance in an area of contact between the upholstery material and the side frames.