A three-piece oil ring and a combination of the three-piece oil ring and a piston, those capable of realizing improved sealing property and reduction in lubrication oil consumption with avoiding generation of sticking even at low tension and thin width of the ring. The three-piece oil ring includes a spacer expander 10 and two side rails. The spacer expander has a radially inner end portion provided with seating tabs 13 protruding in an axial direction and having radially outer inclined surfaces for urging inner peripheral surfaces of the first and second side rails. The spacer expander has a radially outer end portion provided with side rail support portions 14 projecting in the axial direction for supporting axial end faces of the first and second side rails. A seating tab angle of the outer inclined surface relative to an axis is in a range of 10 to 20 degrees, and a ratio of 2X/Y is in a range of from 0.04 to 0.15 where 2X is a total projecting length of the side rail support portions in the axial direction, and Y is a distance between distal end faces of the seating tabs in the axial direction.