Abstract: In this paper, we reported the preparation of high-density polyethylene (PE-HD)/multi-walled carbon nanotubes (MWCNTs) composites through a submerged friction stir processing method, and effects of rotation speed and content of MWCNTs on morphologies and properties of the composites was investigated. The results indicated that MWCNTs were homogeneously dispersed in the matrix in the form of a “cloud”. For the case of the composites containing 1 wt % and 2 wt % of MWCNTs, the tensile strength increased at first and then tended to decrease with an increase of rotational speed. However, the composite containing 4 wt % of MWCNTs exhibited a continuous increase in tensile strength with an increase of rotational speed. A differential scanning calorimetric investigation indicated that the degree of crystallinity of PE-HD was reduced with an increase of the content of MWCNTs.