The orientation of polymer chain has a great effect on its mechanical properties, therefore, it is always an important issue on how to characterize, accurately and quickly, the orientation of polymer chain during processing. In this article, according to the property that ultrasound travels in different velocities in anisotropic media, normal incident shear wave was utilized to explore the orientation structure of HDPE/iPP blends obtained by dynamic packing injection molding. The ultrasonic technique is consistent with the 2D-WAXS in charactering the orientation degree of polymer chains, although ultrasonic technique focuses on the overall orientation of polymer blends while the 2D-WAXS reveals the crystalline orientation of each component. Our work demonstrates that ultrasonic technique might be a reliable, fast and easy way to characterize the orientation structure of crystalline polymer blends. The ultrasonic measurements were performed off-line, but the achievement provides the possibility for on-line detection of orientation structure in injection molding by using ultrasonic technique. (c) 2006 Elsevier Ltd. All rights reserved.