  We consider the fifth order KdV type equations and prove the unconditional
well-posedness in $H^s(\mathbb{T})$ for $s \ge 1$. It is optimal in the sense
that the nonlinear terms can not be defined in the space-time distribution
framework for $s<1$. The main idea is to employ the normal form reduction and a
kinds of cancellation properties to deal with the derivative losses.
