The effect of oxygen plasma treatment on methylsilsesquiazane (MSZ) dielectric was investigated for chemical mechanical planarization (CMP) process. Oxygen plasma treatment was implemented before CMP. Experimental results have shown that the polishing rate of MSZ film with O2 plasma pretreatment is increased as much as two order of magnitude more than that of MSZ without O2 plasma pretreatment. Moreover, the electrical properties of post-CMP MSZ are close to those of an as-cured MSZ. These results indicate that the modified surfaces resulting from O2 plasma treatment increase the polishing rate of MSZ. After polishing, the MSZ film still maintains a low-k quality.