A polishing jig of a hydraulic integral system is improved to increase efficiency. A polishing jig 1 for bearing for use in back-up roll of rolling mill including a shaft member 2 on which an inner ring 104 of a bearing 100 for use in back-up roll of rolling mill is fitted; and a pressure-oil chamber 12 operative in association with the feeding of a pressure oil into the shaft member 2 to protrude an outer circumferential part of the shaft member 2 radially outwardly, the polishing jig includes an inner-ring fixing portion 16 for axially fixing individual inner rings 104 of a plurality of the bearings 100 fitted on the shaft member 2 as axially arranged, wherein a plurality of the pressure-oil chambers 12 are formed internally of the shaft member 2 in correspondence to the plural bearings 100 fixed on the shaft member 2.