  We carried out an international spectroscopic observation campaign of the
dwarf nova GW Librae (GW Lib) during the 2007 superoutburst. Our observation
period covered the rising phase of the superoutburst, maximum, slowly decaying
phase (plateau), and long fading tail after the rapid decline from the plateau.
The spectral features dramatically changed during the observations. In the
rising phase, only absorption lines of H$\alpha$, H$\beta$, and H$\gamma$ were
present. Around the maximum, the spectrum showed singly-peaked emission lines
of H$\alpha$, He I 5876, He I 6678, He II 4686, and C III/N III as well as
absorption lines of Balmer components and He I. These emission lines
significantly weakened in the latter part of the plateau phase. In the fading
tail, all the Balmer lines and He I 6678 were in emission, as observed in
quiescence. We find that the center of the H$\alpha$ emission component was
mostly stable over the whole orbital phase, being consistent with the low
inclination of the system. Comparing with the observational results of WZ Sge
during the 2001 superoutburst, the same type of stars as GW Lib seen with a
high inclination angle, we interpret that the change of the H$\alpha$ profile
before the fading tail phase is attributed to a photoionized region formed at
the outer edge of the accretion disk, irradiated from the white dwarf and inner
disk.
