  We report on a numerical simulation with 2+1 dynamical flavors of overlap
fermions. We calculate pseudo-scalar masses and decay constants on a
$16^3\times 48 \times (0.11 {\rm fm})^4$ lattice at five different up and down
quark masses and two strange quark masses. The lightest pion mass corresponds
to $\approx 310$ MeV. We also study the validity of the chiral perturbation
theory using the results of the numerical simulation with two dynamical flavors
and conclude that the one-loop formulae cannot be directly applied in the
strange quark mass region. We therefore extrapolate our 2+1-flavor results to
the chiral limit by fitting the data to the two-loop formulae of the chiral
perturbation theory.
