A roller bearing, includes an outer race and an inner race coupled together and rotatable relative to each other, the inner and outer race each defining therein a respective rolling channel, each rolling channel defining two raceway faces abutted at right angles, and rollers accommodated in the rolling channels of the inner and outer races and rotatably kept in contact with the raceway faces of the inner and outer races. The roller bearing is characterized in that the inner and outer races each define a groove between the respective two raceway faces thereof; the ratio between the width of each raceway face and the diameter of each roller is ≧0.45 and ≦0.62, thus, the friction resistance between the rollers and the raceway faces is minimized, and therefore, the roller bearing does not wear easily when rotated at a high speed.