  We examine the depairing field $H_{c2}(T)$ of non-centrosymmetric
superconductors with a spin-orbit coupling larger than the Zeeman energy at
$H_{c2}(0)$ by taking account of the mixing of spin-singlet and triplet pairing
states due to the missing parity. When the singlet and triplet pairing
components are mixed with an equal weight in a cubic non-centrosymmetric
system, the paramagnetic depairing effect is significantly suppressed so that
$H_{c2}(T)$ approaches its orbital-limited value. A similar event also occurs
in a quasi two-dimensional Rashba non-centrosymmetric system. The present
results are relevant to the $H$-$T$ phase diagrams of CePt$_3$Si and the
families of Li$_2$Pd$_{3-x}$Pt$_x$B.
