As a basic study of plasma-wall interactions, chemical state of graphite basal face after deuterium bombardment are studied by means of X-ray photoelectron spectroscopy. As the ftuence of deuterium ions with energy of 1 or 4 keY is increased from lOu to 10 18 ions/cm 2 , the C ls line is observed to shift towards the lower binding energy at first, down to the minimum by about 0.2 eV and then towards the higher energy up to an asymptotic value of about 0.2 eV higher than the initial position. The first negative shift is due to lattice displacement at the target surface, and the subsequent positive shift is due to the deuterium trapping at the graphite surface. The fluence dependence of the observed C ls shift is explained by a simple saturation model.