The morphological and microstructural changes during ball milling of PE powder mixed with different weight percent (5–15 wt%) of Alumina particles (50–100 nm) were stud-ied. The milling was performed in a planetary ball mill for various times up to 40 h. The results showed that the addition of hard particles accelerates the milling process, lead-ing to fracture of polyethylene matrix. The result of X-ray diffraction analysis deter-mined that the degree of crystallinity of polyethylene decreased by increasing of ball milling time and weight percent of Alumina.