  We study the Higgs sector of the minimal supersymmetric standard model
extended with vector-like quarks, at the one-loop level. The radiative
corrections to the tree-level masses of the scalar Higgs bosons are calculated
by including the contributions from the loops of top quark, vector-like quarks,
and their scalar superpartners, for a reasonable parameter region. We find that
the mass of the lightest scalar Higgs boson at the one-loop level should be
larger than 85 GeV, if we take into account the negative experimental result
for the Higgs search at LEP2. As the radiative corrections are calculated in
some detail, we also find that the mass of the lightest scalar Higgs boson at
the one-loop level is bounded from above at 280 GeV, This upper bound is
increased from a previous result. It may provide a wider possibility for the
future collider experiments to discover the lightest scalar Higgs boson of this
model.
