  The aim of this paper is to investigate the environment of gamma ray bursts
(GRBs) and the interstellar matter of their host galaxies. We use to this
purpose high resolution spectroscopic observations of the afterglow of
GRB050922C, obtained with UVES/VLT 3.5 hours after the GRB event. We found
that, as for most high resolution spectra of GRBs, the spectrum of the
afterglow of GRB050922C is complex. At least seven components contribute to the
main absorption system at z=2.1992. The detection of lines of neutral elements
like MgI and the detection of fine-structure levels of the ions FeII, SiII and
CII allows us to separate components in the GRB ISM along the line of sight.
Moreover, in addition to the main system, we have analyzed the five intervening
systems between z = 2.077 and z = 1.5664 identified along the GRB line of
sight. GRB afterglow spectra are very complex, but full of information. This
can be used to disentangle the contribution of the different parts of the GRB
host galaxy and to study their properties. Our metallicity estimates agree with
the scenario of GRBs exploding in low metallicity galaxies
