  In this paper we explain the diphoton excess in the invariant mass M
$\approx$ 750 GeV , claimed by the ATLAS and CMS collaborations at the run-2
LHC, as the signal of a scalar singlet in a string inspired exceptional
supersymmetric standard model (ESSM). The scalar singlet might play a rule in
the spontaneous breaking of the $U(1)^\prime$ gauge symmetry of the ESSM and
couples to diphoton and/or gluon pair with the help of exotic quarks and
Higgs-like supermultiplets, which are contained in the fundamental
representation of the $E_6$ group. The model might give rise to a large enough
production cross section at the LHC but can hardly fit with the wide width of
the resonance except in the strong couple regime.
