A bearing (100) has a contact surface (110) for mating with a rotatable member. The contact surface has a plurality of crystalline grains (120) distributed at random; a plurality of micro-grooves (130) are formed among the crystalline grains; the micro-grooves communicate with each other thereby forming a net. The micro-grooves accommodate lubricant therein so that when the rotatable member rotates, a sufficient lubrication can be obtained between the bearing and the rotatable member. The bearing is formed by machining and then thermally etching a preform which is formed by powder metallurgy.