In this study, a noninvasive and nondestructive ultrasonic technique has been used to monitor the polymer injection-molding process in an attempt to establish a fundamental understanding of the processing/morphology/ultrasonic signal relationships. The ultrasonic technique not only can provide information on solidification affected by various temperatures and pressures but also can reflect the evolution of the crystal morphology and phase morphology of polymer blends. In addition, the periodic vibration of the dynamic-packing injection-molding process, in which the melt is forced to move repeatedly in a chamber by two pistons that move reversibly with the same frequency as the solidification progressively occurs from the mold wall to the molding core part, can also be monitored with the ultrasonic velocity and attenuation. Our results indicate that the ultrasonic technique is sensitive and promising for the real-time monitoring of the injection-molding process. (C) 2007 Wiley Periodicals, Inc.