  Radiative corrections to ${\rm e}^{+}{\rm e}^{-}\! \rightarrow {\rm
W}^{+}{\rm W}^{-}$ from Majorana neutrinos are studied in the context of the
see-saw mechanism. Focusing on the effects of the fourth generation neutrinos,
we calculate W-pair form factors, the differential cross sections and the
forward-backward asymmetries for the polarized electrons at one-loop level. The
behaviour of the form factors at the threshold of Majorana particle pair
productions is found to differ from that of Dirac particle pair productions. In
the cross section for unpolarized electrons, the radiative corrections,
depending on the mass parameters of the see-saw mechanism, are found to be
$\sim 0.5\%$ at the energy range of the LEP200 and the next generation linear
colliders.
