When viscoelastic fluids are extruded through the nozzles and the flow velocity exceeds a critical velocity, it is widely known that the fluids flow out with anomalous shapes, so called melt fracture. This paper deals with geometrical dimensions of extruded polyethylenes with roughly regular shapes in order to verify fundamental causes of occurrence for those anomalous phenomena among melt fracture, so called the "spiraling" and the "wrinkling". It was found, as a result, that one of the causes of the wrinkling was due to fluctuation of the flow rate yielded by the mixing pins usually installed on ohe downstream end of the screw shaft. It was also found that the spiraling had two kinds of phenomena, one was extruding with small pitch like the triangular thread and the other large, and this anomalous phenomena occurred at the same working condition.
