  The neutral intergalactic medium in the post reionization epoch allows us to
study cosmological structure formation through the observation of the
redshifted 21 cm signal and the Lyman-alpha forest. We investigate the
possibility of measuring the total neutrino mass through the suppression of
power in the matter power spectrum. We investigate the possibility of measuring
the neutrino mass through its imprint on the cross-correlation power spectrum
of the 21-cm signal and the Lyman-alpha forest. We consider a
radio-interferometric measurement of the 21 cm signal with a SKA1-mid like
radio telescope and a BOSS like Lyman-alpha forest survey. A Fisher matrix
analysis shows that at the fiducial redshift z = 2.5, a 10,000 hrs 21-cm
observation distributed equally over 25 radio pointings and a Lyman-alpha
forest survey with 30 quasars lines of sights in 1 {deg}^2, allows us to
measure \Omega_{\nu} at a 3.25 % level. A total of 25,000 hrs
radio-interferometric observation distributed equally over 25 radio pointings
and a Lyman-alpha survey with \bar n = 60 {\rm deg}^{-2} will allow
\Omega_{\nu} to be measured at a 2.26 % level. This corresponds to an idealized
measurement of \sum m_{\nu} at the precision of (100 \pm 2.26) meV and f_{\nu}=
\Omega_{\nu}/ \Omega_{m} at 2.49 % level.
