Understanding the cosmic re-ionization is one of the key goals of the modern observational cosmology .
High redshift QSO spectra can be used as background light sources to measure absorption by intervening neutral hydrogen .
We investigate neutral hydrogen absorption in a deep , moderate-resolution Keck/Deimos spectrum of QSO CFHQSJ2329-0301 at z=6.4 .
This QSO is one of the highest redshift QSOs presently known at z=6.4 but is 2.5 mag fainter than a previously well-studied QSO SDSSJ1148+5251 at z=6.4 .
Therefore , it has a smaller Stromgren sphere , and allows us to probe the highest redshift hydrogen absorption to date .
The average transmitted flux at 5.915 < z _ { abs } < 6.365 ( 200 comoving Mpc ) is consistent with zero , in Ly \alpha , Ly \beta , and Ly \gamma absorption measurements .
This corresponds to the lower limit of optical depth , \tau _ { eff } ^ { \alpha } > 4.9 .
These results are consistent with strong evolution of the optical depth at z > 5.7 .