Electrostatic charging of oxygen-terminated nanocrystalline diamond (NCD) thin films deposited on silicon in sub-100nm thickness and with intentionally high relative sp 2 phase ratio (60%) is characterized on a microscopic level. By correlating Kelvin Force Microscopy, Current-Sensing Atomic Force Microscopy, micro-Raman spectroscopy and cross-sectional Scanning Electron Microscopy data we show that the charging is determined by both the surface topography (grains and grain boundaries) and complex sub-surface morphology (arrangement of grains and sp 2 phase) on scales below 2×2μm 2 . These microscopic data and macroscopic I(V) characteristics evidence that sp 2 phase dominates over diamond grains in local electrostatic charging of NCD thin films. Moreover, the tip-surface junction quality is identified as the main factor behind large variations (0.1 to 1V) of the overall induced electrostatic charge contrast.