We calculate the neutral B meson mixing matrix elements and their SU(3)f breakink ratio ξ using domain-wall light and static heavy quarks. O(αs a) corrections are taken into account so the remaining discretization error is O(a2). Phenomenologically the most valuable parameter in our calculation is ξ , the ratio of the matrix elements with B0d and B0s, which provides an important constraint on the apex of the unitarity triangle. In the ratio, a large fraction of statistical error as well as various systematic errors cancel. We expect a few percent errors for lattice discretization and 1/mb errors. We analyze both unitary and partially quenched valence down and strange quark mass points on about 200 configurations for each ensemble of the Nf=2+1 domain wall fermions with a ≃ 0.11 fm and 243 volume generated by RBC and UKQCD collaborations. By these measurements we expect that the statistical and chiral extrapolation errors on ξ can be alleviated to the level of the other systematic errors.