  The top/bottom seesaw model, which extends the top seesaw in order to
accomodate a 125 GeV Higgs boson, predicts vector-like top/bottom partners and
these partners can be bounded to form several neutral and charged singlet
composite scalars by some new strong dynamics. In this letter, we use such a
singlet scalar to interpret the 750 GeV diphoton reseanance. This singlet
scalar is dominantly produced through the gluon fusion process induced by the
partners and its diphoton decay is induced by both the partners and the charged
singlet scalars. We show that this scenario can readily account for the
observed 750 GeV diphoton signal under the current LHC constraints. Further,
this scenario predicts some other phenomenology, such as a strong correlation
between the decays to $\gamma\gamma$, $Z \gamma$ and $ZZ$, a three-photon
singal from the associate production of a singlet scalar and a photon, as well
as some signals from the partner cascade decays. These signals may jointly
allow for a test of this framework in future LHC and ILC experiments.
