Cast metal parts are extensively found in many engineering products such as pump casing and engines. Thermal effects exhibited during metal casting processes, such as solidification can generate defects in the cast components. Effective nondestructive testing (NDT) for detection and sizing of defects in cast parts prevents extra cost and time associated with repair and maintenance. Surface-breaking cracks and porosity are among the common types of defects in large cast components. There are several limitations in using conventional NDT methods for as built cast parts due to surface conditions, coarse-grain structure, and characteristics of potential defects. Ultrasonic adaptive imaging based on the Phased Array Ultrasonic Testing (PAUT) technology is proposed for coarse-grain heavy-walled cast material inspection. The capability of aperture focusing in PAUT provides the opportunity for better imaging results. A comprehensive understanding about the ultrasonic beam focusing and the selection of an appropriate transducer and wedges is necessary for successful defect characterization. Cast aluminum and iron samples having on-purpose made defects were successfully inspected using the PAUT. Unlike conventional techniques, the results indicated that the PAUT is a promising method for inspecting as-built cast parts with rough surface finish conditions. The proposed method helps to decrease the inspection time, machining requirements, and preparation costs. Moreover, the enhanced defect sizing approach provides useful information for repair and maintenance decision making such as amount of material grinding and post-welding procedure.