  We calculate the QCD corrected effective Hamiltonian for $B\bbar$--Mixing in
heavy quark effective theory including corrections of the order $\Lambda_{QCD}
/ m_b$. The matrix elements of the subleading operators are estimated using the
vacuum insertion assumption. We show that the major part of the subleading
corrections may be absorbed into the heavy meson decay constant $f_B$; the
remaining corrections are only due to QCD effects and give an enhancement of
$\Delta M$ of 5\%.
