  We propose a new method for determining total masses of low frequency
eccentric binaries (such as, neutron star binaries with orbital frequency
$f\gsim 10^{-3}$Hz) from their gravitational waves.
  In this method we use the frequency shift caused by periastron advance, and
it works even at low frequency band where chirp signal due to radiation
reaction is difficult to be measured. It is shown that the total masses of
several Galactic neutron star binaries might be measured accurately (within a
few percent error) by LISA with operation period of $\sim 10$ years.
