In order to identify the optical counterparts of X-ray AGN, we take into account the magnitude distribution of X-ray sources hosts, which is different from that of the confusing background sources. The estimated fraction (y-axis) of X-ray AGN having an optical counterpart with i-band below magnitude m(x-axis), has been determined using a Monte-Carlo simulation (see Tasse et al. 2008b, for the details). Around 76%of X-ray sources have an optical counterpart at the limiting magnitude of our survey (the vertical dotted line shows the 80% completeness level of the optical survey).