  This paper presents a first study of the masses and decay constants of the
charged, or flavor-off-diagonal, pseudoscalar mesons to two loops for two
flavors of sea-quarks, in Partially Quenched Chiral Perturbation Theory
(PQ$\chi$PT). Explicit analytical expressions up to ${\cal O}(p^6)$ in the
momentum expansion are given. The calculations have been performed within the
supersymmetric formulation of PQ$\chi$PT. A numerical analysis is done to
indicate the size of the corrections.
