The effect of Chemical Mechanical Modification (CMM) on the $$zeta-potential and size distribution of nanodiamonds was studied. Results show significant change in the functional groups on its surface after the CMM treatment by the anionic surface modifier DN-10. The amount of hydroxyl groups decreases and two peaks connected with the stretching vibration of carboxylate appear instead of those of carbonyl. The $$zeta-potential goes up significantly and the size drops to some extent. If treated further with CMM1, a new absorption peak 1382.19 cm$-1$ connected with the vibration of some distinctive functional groups which cause the increase in the $$zeta-potential and the decrease in size appears.