Non-destructive testing using ultrasonic measurement is used to ensure the quality of the die-casting products. The quality of a casting depends on the presence of discontinuities such as porosity and on the final metallurgical structure. Discontinuities occurring in the sub-surface of the cast structure mostly have irregular surfaces which scatter the ultrasound waves and make ultrasonic testing more difficult. The effective use of ultrasonic testing for inspection of castings depends greatly upon the skills and expertise of the operator. However, the initial experimental set-up is important to develop a proper inspection procedure that is easily understood by the operators. The aim of the present work is to investigate and develop an automated ultrasonic inspection system for detecting sub-surface defects in aluminium die-casting parts. Two sample test cases were selected from the industrial partners. Ultrasonic immersion testing was carried out on the sample parts using different probes situated at different water path distances to obtain the best possible signal from the defect. The results obtained from the experiments have demonstrated the feasibility of developing an online automatic inspection system to detect sub-surface defects in aluminium die-casting components.