A lens for an optical recording and reproducing system includes: a plane of incidence on which a light generated from a light source is made incident; a first reflection side for reflecting a light passing through a plane of incidence; and a second reflection side for reflecting again the light that has been reflected on the first reflection side, the second reflection side being coated with a reflection material and being formed to be parabolic. The lens for an optical recording and reproducing system is very small in its size and weight, compared to the conventional lens for an optical recording system. In addition, the lens has a large numerical aperture and a less light loss by using one focussing lens without an objective lens, so that an information recording and reproducing efficiency can be heightened. Moreover, the height of the lens and the overall system where the lens is mounted can be remarkably reduced, so that the present invention provides an ultra-thin optical recording system that can be employed for a mobile instrument.