This work studies the effect of PE-g-MA compatibilizer on mechanical thermal and morphological properties of high density polyethylene (HDPE)/titanium dioxide (TiO2) nanocomposites. The HDPE/TiO2 nanocomposites with and without PE-g-MA compatibilizer were prepared by melt mixing technique in a twin screw extruder. The results found that Young's Modulus of HDPE/TiO2 nanocomposites increased with increasing TiO2 contents. The addition of PE-g-MA compatibilizer had no significant effect on the tensile strength and stress at break of HDPE/TiO2 nanocomposites. The decomposition temperatures of HDPE/TiO2 nanocomposites before and after adding PE-g-MA compatibilizer increased with increasing TiO2 contents. The dispersion of TiO2 nanoparticles in HDPE matrix was observed by scanning electron microscope (SEM). The dispersion of nanoparticles in HDPE matrix with PE-g-MA compatibilizer was relatively good, only a few aggregates exited.