Internal casting defects that are detected by radiography may also be detected by ultrasonic method. Ultrasonic testing allows investigation of the cross-sectional area of a casting, it is considered to be a volumetric inspection method. The high frequency acoustic energy travels through the casting until it hits the opposite surface or an interface or defect. The interface or defect reflects portions of the energy, which are collected in a receiving unit and displayed for the analyst to view. The pattern of the energy deflection can indicate internal defect. Ultrasonic casting testing is very complicated in practice. The complications are mainly due to the coarse-grain structure of the casting that causes a high ultrasound attenuation. High attenuation then makes it impossible to test the entire volume of material. This article is focused on measurement of attenuation, the effect of probe frequency on attenuation and testing results.