  We investigate instantons in finite temperature QCD via Witten's holographic
QCD. To study the deconfinement phase, we use the setup proposed in [1]
(arXiv:1107.4048). We find that the sizes of the instantons are stabilized at
certain values both in the confinement and deconfinement phases. This agrees
with the numerical result in the lattice gauge theory. Besides we find that the
gravity duals of the large and small instantons in the deconfinement phase have
different topologies. We also argue that the fluctuation of the topological
charges is large in confinement phase while it is exponentially suppressed in
deconfinement phase, and a continuous transition occurs at the
Gross-Witten-Wadia (GWW) point. It would be difficult to observe the
counterpart of this transition in lattice QCD, since the GWW point in QCD may
stay at an unstable branch.
