The effect of surface modification on the mechanical properties and microstructure of the composites of high-density polyethylene (HDPE), silicone oil, and aluminum hydroxide [Al(OH)(3)] was investigated. The dispersion of silicone oil in the HDPE composites was studied by scanning electric microscope (SEND and differential scanning calorimetry (DSC). In the HDPE/Al(OH)(3)/silicone oil composites, two types of dispersion structure of silicone oil were observed resulting from different surface modifications. In the composites surface modified with titanate NDZ-130, calcium stearate, or oleic acid, silicone oil encapsulates around Al(OH)(3) particles, and both the notched impact strength and the elongation at break are very high. However, in the composites surface modified with silane KH-550 or silane-g-HDPE, silicone oil and Al(OH)(3) particles separately disperse in HDPE, and both the notched impact strength and the elongation at break are very low.