The gravity die casting of the AC4C aluminum alloy was conducted when mechanical vibration was incorporated. The specimen with a specification of 25 mm in diameter and 210 mm in length were solidified at various vibration frequencies so as to examine the effect of the vibration on the grain size, the casting defect distribution, and mechanical properties. In comparison with the grains formed in the as-cast state without vibration, the grains in the inner area of a specimen became finer after mechanical vibration. The columnar structure remained in its outer region under all vibration frequency. The average density of specimen increased by imposition the mechanical vibration. The casting defects involved in the specimen reduced and became smaller with the increase of vibration frequency. The scattering in mechanical properties of specimens cast with mechanical vibration decreased because of the decrease in casting defects. [doi:10.2320/matertrans.F-M2009822]