A lubricating system for a valve seat of an internal combustion engine produces a lubricant oil film on the valve seat (7) of a seat ring (2) providing the valve seat. At least a part of the seat ring (2) providing the valve seat surface (7) is made of a porous material (6, 9) readily containing lubricant oil. The outer cylindrical surface of the seat ring (2) is formed with an annular groove (4) along its circumferential direction. A cylinder head (1) to which the seat ring (2) is fastened is formed with an oil passage (5) for feeding lubricant oil to the groove (4). Feeding of the lubricant oil through the oil passage (5) to the groove (4) causes the valve seat surface (7) providing the part of the seat ring (6, 9) made of the porous material to contain lubricant oil. The lubricant oil thus contained produces a lubricant oil film on the valve seat surface (7), which prevents wear in the valve head and the valve seat surface.