  We study the single top production mediated by flavor changing neutral
current via both of the $t-q-\gamma$ and $t-q-Z$ vertices (here q represents c
and u quarks) in ep collisions at two colliders HERA and THERA. Contribution of
the second vertex becomes even more important as the couplings take more
improved values provided by the higher luminosities of colliders. In addition
to these improvements if the CM energy of the collider is increased, the
production will be dominated by the anomalous $t-q-Z$ vertex.
