  We have studied the Kaluza-Klein (KK) mode contributions to the diphoton
decay of Higgs boson through the gluon fusion at LHC in a five dimensional
$SU(3) times U(1)'$ gauge-Higgs unification (GHU) model. The minimal matter
content case is found that the diphoton decay is necessarily destructive
comparing to the Standard Model (SM) prediction, which is unfortunately not
supported by the current experimental data. Two extensions are considered to
not only enhance the diphoton decay but also realize an observed Higgs mass.
The $Z gamma$ decay of Higgs boson is also studied and the striking result is
found that there is no KK mode contributions to the decay at 1-loop level. This
fact might be very useful to discriminate the GHU from other physics beyond the
SM.
