  We show that the low energy effective model derived from SU(5) with 45-plet
Higgs can account for the recently reported enhanced diphoton decay rate of the
Standard Model (SM)-like Higgs with mass about 125 GeV. This model extends the
SM by an extra Higgs doublet and color-octet scalar doublet. We show that the
charged octet scalars are not severely constrained by flavor changing neutral
current and can be light. However, the K^0-\bar{K}^0 mixing implies that the
neutral octet-scalar mass should be larger than 400 GeV for \tan\beta ~ O(1).
The role of charged octet scalar in the loop of Higgs decay into diphoton is
investigated . We point out that the most significant impact of this model on
the diphoton decay width comes from the suppression of top-quark coupling with
SM-like Higgs or even flipping its sign that leads to important enhancement in
\Gamma(h -> gamma gamma). We also study the implications of the neutral
octet-scalar contributions to the gluon fusion Higgs production cross section
in alleviating the apparent tension between enhancement of diphoton decay rate
and suppression of \sigma(gg -> h).
