Disclosed is a mat for exercise. The mat comprises a main mat having a foot hanger for a sit-up at a top surface of one side thereof and a plurality of grooves at a bottom surface of both lateral sides thereof, a plurality of sub-mats coupled with the main mat in use, and a plurality of attachment plates installed at corners of a bottom surface of the main mat and corners of bottom surfaces of the sub-mats, wherein the main mat is provided with female fabric hook-and-loop fastener (e.g., Velcro) tapes mounted at the grooves thereof, and the sub-mat is provided with male fabric hook-and-loop fastener (e.g., Velcro) tapes that laterally protrude corresponding to the grooves of the main mat.