When the magnetic field is applied to magnetic or MR fluids, some of inner particles form clustering structure. These clustering structures influence on the ultrasonic propagation velocity in these fluids. We measured precisely the properties of ultrasonic propagation velocity in these fluids subjected to the magnetic field. The measurement scheme is based on the pulse method. The external magnetic field intensity is varied from 0 mT to 550 mT and the angle between the magnetic field direction and the direction of ultrasonic wave propagation is varied from 0° to 90°. Some interesting properties of ultrasonic propagation such as hysteresis and anisotropy are observed. Based on the experimental results, the inner structures of the magnetic or the MR fluids are analyzed experimentally and the application of non-contact inspection in these fluids by ultrasonic techniques is discussed.