  We study the $\kappa$ meson in 2+1 flavor QCD with sufficiently light $u/d$
quarks. Using numerical simulation we measure the point-to-point $\kappa$
correlators in the "Asqtad" improved staggered fermion formulation. We analyze
those correlators using the rooted staggered chiral perturbation theory
(rS$\chi$PT), particular attention is paid to the bubble contribution. After
chiral extrapolation, we obtain the physical $\kappa$ mass with $828\pm97$ MeV,
which is within the recent experimental value $800\sim900$MeV. These numerical
simulations are carried out with MILC 2+1 flavor gauge configurations at
lattice spacing $a \approx 0.12$ fm.
