An adjustable back-lighting structure for a keyboard includes a light guide panel having vertical peripheral edges and at least one light entering surface; and a surrounding edge made of plastic or chemical macromolecule compound material, having a connecting interface tightly bonded with the vertical peripheral edges of the light guide panel. The connecting interface can generates the feedback beam Bf to enhance the illumination effect. Therefore, the light transmission in the light guide panel can be limited in the upper and lower surfaces without leakage at the vertical peripheral edges.