  We examine effects of $Z'$ bosons in gauge-Higgs unification (GHU) models at
$\mathrm{e}^{+}\mathrm{e}^{-}\to \mathrm{e}^{+}\mathrm{e}^{-}$ Bhabha
scatterings. We evaluate differential cross sections in Bhabha scatterings
including $Z'$ bosons in two types of $\mathrm{SO}(5) \times \mathrm{U}(1)
\times \mathrm{SU}(3)$ GHU models. We find that deviations of differential
cross sections in the GHU models from those in the SM can be seen at $\sqrt{s}
= 250\,\mathrm{GeV}$. With $80\%$-longitudinally polarized electron and
$30\%$-longitudinally polarized positron beams, the left-right asymmetries in
the GHU A- and B-models are resolved at more than $3\,\sigma$ at $L_{\rm int}
=250\,\mathrm{fb}^{-1}$. We also show that Bhabha scattering with scattering
angle less than 100 mrad can be safely used as luminosity measurements in
$\mathrm{e}^{+}\mathrm{e}^{-}$ colliders since the effects of $Z'$ bosons are
well suppressed for small scattering angle. We propose a new observable which
can be measured at future TeV-scale $\mathrm{e}^{+} \mathrm{e}^{-}$ linear
colliders.
