Grand Unified Theory (GUT) can unify not only three gauge forces in the Standard Model (SM)
into a single gauge force but also quarks and leptons in the SM into a few multiplets.
Interestingly, for both unifications, we have already signatures from the experiments.
For the unification of forces, we have gauge coupling unification as a signature.
Moreover,  the measured masses and mixings are consistent with the unification of matters.
Only one assumption that 10 dim. fields induce stronger hierarchy for the Yukawa couplings
than 5bar fields, can explain various hierarchies of quark and lepton masses and mixings.
E6 GUT is attractive because the assumption can be obtained as a result. E6 GUT can explain
the various hierarchies of quark and lepton masses and mixings so naturally that we can build a
model in which all three generation of quarks and leptons can be unified into a single multiplet
while realistic quark and lepton masses and mixings can be obtained by breaking the family
symmetry. We discuss the signatures of this E6 GUT in future, nucleon decay and sfermion
mass spectrum. We briefly comment LHC results in the scenario, especially the weak scale
stability problem.