We investigate the chiral properties of quenched domain-wall QCD (DWQCD) at the lattice spacings $a^{-1} simeq 1$ and 2 GeV for both plaquette and renormalization-group (RG) improved gauge actions. In the case of the plaquette action we find that the quark mass defined through the axial Ward-Takahashi identity remains non-vanishing in the DWQCD chiral limit that the bare quark mass $m_fto 0$ and the length of the fifth dimension $N_stoinfty$, indicating that chiral symmetry is not realized with quenched DWQCD up to $a^{-1} simeq 2$ GeV. The behavior is much improved for the RG-improved gauge action: while a non-vanishing quark mass remains in the chiral limit at $a^{-1}simeq 1$ GeV, the result at $a^{-1}simeq 2$ GeV is consistent with an exponentially vanishing quark mass in the DWQCD chiral limit, indicating the realization of exact chiral symmetry. An interpretation and implications are briefly discussed.
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