A new type of extrusion apparatus with a hydraulic vibration field was self-developed to study the effects of vibration on the rheological behavior, mechanical properties, and morphology of high-density polyethylene (HDPE) during the process of extrusion. In the research, the morphology and mechanical properties of specimens produced by conventional extrusion molding were used for comparison with specimens obtained via vibration extrusion molding. The research showed that the extrusion property of the HDPE melt was improved under a vibration field, and the apparent viscosity decreased. The maximum decrement of the apparent viscosity was 37.98%. The change in the apparent viscosity of the HDPE melt corresponded to the vibration frequency and amplitude, die temperature, and rotational speed of the extruder screw. Both the longitudinal and transverse yield strengths of the HDPE specimens increased under the vibration field. The increment of the longitudinal yield strength (11.5%) was bigger than that of the transverse yield strength (6.9%). According to scanning electron microscopy micrographs, the vibration field made the crystallites orient and become smaller, and the crystal size became more homogeneous. (C) 2007 Wiley Periodicals, Inc.