  We discuss the constraint on the size of QCD instanton effects in low-energy
effective theory. Among various instanton effects in meson mass spectrum and
dynamics, we concentrate on the instanton-induced masses of light quarks. The
famous instanton-induced six-quark interaction, so-called 't Hooft vertex,
could give non-perturbative quantum corrections to light quark masses. Many
works have already been achieved to constrain the mass corrections in light
meson system, or the system of pi, K, eta and eta', and now we know for a fact
that the instanton-induced mass of up-quark is too small to realize the
solution of the strong CP problem by vanishing current mass of up-quark. In
this work we give a constraint on the instanton-induced mass correction to
light quarks from the mass spectrum of heavy mesons, B+, B0, Bs and their
anti-particles. To accomplish this, the complete second order chiral symmetry
breaking terms are identified in heavy meson effective theory. We find that the
strength of the constraint from heavy meson masses is at the same level of that
from light mesons, and it would be made even stronger by more precise data from
future B factories and lattice calculations.
