Blends of ultrahigh molecular weight polyethylene (UHMWPE) chopped fibers with high density polyethylene (HDPE) were prepared by melt mixing extrusion, followed by melt drawing. The combined effect of composition and flow on the morphology was investigated by microbeam synchrotron X-ray diffraction and high resolution scanning electron microscopy. Apparently in the drawn blends, the presence of fibers resulted in a higher degree of orientated morphology and-as revealed by differential scanning calorimetry-higher degrees of crystallinity and melting points. Significant improvement of mechanical properties was observed with increase of the fiber volume fraction. These results indicate that the oriented arrays of immiscible UHMWPE domains aligned in the flow direction, joined by fiber-induced crystallization of the surrounding ADPE matrix, and provide strong reinforcing effect.