  We formulate and establish a super duality which connects parabolic
categories $O$ between the ortho-symplectic Lie superalgebras and classical Lie
algebras of $BCD$ types. This provides a complete and conceptual solution of
the irreducible character problem for the ortho-symplectic Lie superalgebras in
a parabolic category $O$, which includes all finite-dimensional irreducible
modules, in terms of classical Kazhdan-Lusztig polynomials.
