The formation of multilayer structures in the high-speed thin wall injection-molded samples of high-density polyethylene/isotactic polypropylene blends is reported. Based on the morphology development in injection runner and mold, a possible formation mechanism of multilayer structure was proposed in this study. Injection molding could be used as a simple and an effective method for the fabrication of multifunctional multilayer structure. This work is interesting and important for scientific research as well as several potential applications. (c) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011