Chemical/mechanical polishing can be used to polish the rough surface of diamond films prepared by chemical vapor deposition (CVD). In this paper, a mixture of oxidizing agents (LiNO 3 02+02KNO 3 ) has been introduced to improve the material removal rate and the surface roughness in chemical/mechanical polishing because of its lower melting point. It had been shown that by using this mixture the surface roughness R a (arithmetic average roughness) could be reduced from 8–17 to 0.4 μm in 3 h of polishing, and the material removal rate can reach 1.7–2.3 mg/cm 2 /h at the temperature of 623 K. Pure aluminium is compared with cast iron as the contact disk material in the polishing. Although the material removal rate of aluminiumdisk is lower than that of cast iron, it can eliminate the carbon contamination from the contact disk to the surface of diamond films, and facilitate the analysis of the status of diamond in the chemical/mechanical polishing. The surface character and material removal rate of diamond films under different polishing pressure and rotating speed have also been studied. Graphite and amorphous carbon were detected on the surface of polished diamond films by Raman spectroscopy. It has been found that the oxidization and graphitization combined with mechanical cracking account for the high material removal rate in chemical/mechanical polishing of diamond films.