  We compute non-perturbatively the B-parameters of the complete basis of
four-fermion operators needed to study the Kaon oscillations in the SM and in
its supersymmetric extension. We perform numerical simulations with two
dynamical maximally twisted sea quarks at three values of the lattice spacing
on configurations generated by the ETMC. Unwanted operator mixings and O(a)
discretization effects are removed by discretizing the valence quarks with a
suitable Osterwalder-Seiler variant of the Twisted Mass action. Operators are
renormalized non-perturbatively in the RI/MOM scheme. Our preliminary result
for BK(RGI) is 0.73(3)(3).
