  We revisit the minimal Nambu-Goldstone (NG) Higgs supersymmetric (SUSY) SU(5)
grand unified model and study its phenomenological implications. The Higgs
sector of the model possesses a global SU(6) symmetry, which is spontaneously
broken and results in the Higgs doublets of the minimal SUSY Standard Model
(MSSM) as NG chiral superfields. Therefore, the model naturally leads to light
Higgs doublets and solves the doublet-triplet splitting problem. Because of the
SU(6) symmetry, the couplings of the Higgs sector are tightly restricted, and
thus the model is more predictive than the minimal SUSY SU(5). We determine all
the grand-unified-theory parameters via the matching conditions of the gauge
coupling constants at the unification scale and calculate proton lifetime,
confronting this with current experimental bounds. We discuss that this model
is incompatible with the constrained MSSM, whilst it has a large viable
parameter space in the high-scale SUSY scenario. The perturbativity condition
on the trilinear coupling of the adjoint Higgs field imposes an upper (lower)
limit on the wino (gluino) mass, implying a hierarchical mass pattern for these
gauginos. Future proton-decay searches can probe a large part of the parameter
space, especially if the SUSY-breaking scale is $\lesssim 100$~TeV.
