This research aims to inspect the defects and discontinuities in steel billet by ultrasonic detector. Straight beam probe used to detect a lot number of imported steel billets that clearly have internal defects. The results showed the possibility of initial detection by straight beam probe, and initial defining the types of defects such as, micro and macro cracks, shrinkage defect, blow holing, inclusion, porosity and others type of internal defects. The experiments showed that if the necessity is defining the size of defects, this requires angle beam probe in addition to straight beam probe.