This study describes the effect of surfactant concentration on the chemical mechanical polishing process of Ge1Sb6Te3 film using nanodiamond-based slurry. Aggregated diamond nanoparticles were dispersed in a slurry solution containing anionic poly(sodium 4-styrene sulfonate) using milling system. The zeta-potential, particle size and transmission electron microscopy image of the dispersed nanodiamond particles were analyzed for slurries having varying surfactant concentrations to identify the effect of the surfactant concentration on the milling process. The cationic nanodiamond particles were covered with the anionic poly(sodium 4-styrene sulfonate) polymer, and the polymer acted as a dispersion agent on account of the electrostatic repulsion. By increasing the surfactant concentration in the milling process, the average particle size of the nanodiamond particle decreased until the concentration reached 0.9 wt%. In addition, the surface roughness and material removal rate of the Ge1Sb6Te3 film in the polishing process strongly-depended on the surfactant concentration. Both surface roughness and material removal rate decreased with an increase in the surfactant concentration. Excess poly(sodium 4-styrene sulfonate) acted as a passivation layer, resulting in a decrease in the surface roughness and material removal rate of the Ge1Sb6Te3 film.