PURPOSE: A heat exchanger for air conditioner is provided to facilitate turbulent flow of air and improve heat transfer performance and efficiency by forming a plurality of cantilever-shaped slits at the flat fin. CONSTITUTION: A heat exchanger comprises a plurality of flat fins(1) arranged to be parallel with each other and at a predetermined spacing to permit the air to flow between flat fins; and a plurality of heat transfer tubes(2) inserted perpendicularly to the flat fin such that the fluid flowing through the heat transfer pipe is heat exchanged with the air contacting the flat fin. The flat fin has a plurality of cantilever-shaped slit groups(100) which are formed to be opened at the same time both in the flow direction of the air flowing along the surface of the flat fin and in the direction perpendicular to the air flow direction.
