  In gauge-Higgs unification (GHU), the 4D Higgs boson appears as a part of the
fifth dimensional component of 5D gauge field. Recently, an $SO(11)$ GUT
inspired $SO(5)\times U(1)\times SU(3)$ GHU model has been proposed. In the
GHU, Kaluza-Klein (KK) excited states of neutral vector bosons, photon, $Z$
boson and $Z_R$ boson, appear as neutral massive vector bosons $Z'$s. The $Z'$
bosons in the GHU couple to quarks and leptons with large parity violation,
which leads to distinctive polarization dependence in, e.g., cross sections and
forward-backward asymmetries in $e^-e^+\to\mu^-\mu^+,q\bar{q}$ processes. In
the talk, we discuss fermion pair production in $e^-e^+$ linear collider
experiments with polarized $e^-$ and $e^+$ beams in the GUT inspired GHU.
Deviations from the SM are shown in the early stage of planned international
linear collider (ILC) with 250 GeV experiments. The deviations can be tested
for the KK mass scale up to about 15 TeV. This talk is mainly based on
Phys.Rev.D102(2020)015029.
