Abstract: An apparatus for securing a fin to the bottom surface of a surfboard and comprising a uniquely configured fin box designed to provide a more secure structural relationship between the fin box and the surfboard. The invention is also designed to provide a more secure means for securing the fin within the fin box to prevent inadvertent loss of the fin while still providing a more advantageous means for releasing the fin from the fin box when removal of the fin is desirable. More specifically, the present invention comprises a fin box of substantially rectangular configuration and designed to be embedded within the underlying surface of the surfboard whereby the exterior surface of the fin box lies flush with the exterior underlying surface of the surfboard. A novel flange integral with the fin box is included to provide added structural resistance to transverse forces that normally occur during surfing which would otherwise tend to cause rotation and loosening of the fin box within the surfboard.