In recent years, the popularity of intramedullary humeral nailing is on the rise in spite of its handicaps. There are many problems in intramedullary humeral. stabilization because of the anatomic structure of the bone. We performed various methods and measurements to determine shape, length and diameter and curvature of the medullary canal of the humerus in 57 human dry cadaver bones. Anterior angulation with an average of 21 cm apart from greater tubercle was found at 1/3 distal part. Mean degree of angulation was 9degrees (max: 15, minutes: 5, S.D.: 2.84). Humerus bones with septal aperture (supratrochlear foramen) at the fossa coronoidea were observed to have very narrow medullary canal. The best point for nail insertion was found to be an area on the line from greater tubercle anteromedially to caput humeri. This study revealed that carefully evaluated structure of humeral medullary canal and various congenital constructions such as septal aperture, and correct selection of a nail with proper length and diameter are essential for successful nailing.