  The SU(5) GUT model extended with fermions in the adjoint $24_F$
representation predicts triplet fermions in the 100 GeV mass range, opening up
the possibility of testing seesaw at LHC. However, once the model is
supersymmerized, the triplet fermion mass is constrained to be close to the GUT
scale for the gauge couplings to unify. We propose an extension of the SUSY
SU(5) model where type II seesaw can be tested at LHC. In this model we add a
matter chiral field in the adjoint $\hat{24}_F$ representation and Higgs chiral
superfields in the symmetric $\hat{15}_H$ and $\hat{\bar{15}}_H$
representations. We call this the symmetric adjoint SUSY SU(5) model. The
triplet scalar and triplet fermion masses in this model are predicted to be in
the 100 GeV and $10^{13}$ GeV range respectively, while the mass of the singlet
fermion remains unconstrained. This gives a type I plus type II plus type III
seesaw mass term for the neutrinos. The triplet scalars with masses $\sim 100$
GeV range can be produced at the LHC. We briefly discuss the collider
phenomenology and predictions for proton decay in this model.
