  SU(2)-flavor-symmetry breaking in antiquark distributions of the nucleon was
suggested by the New Muon Collaboration (NMC) in deep inelastic muon
scattering. As an independent test, Drell-Yan data for the tungsten target have
been used for examining the asymmetry. We investigate whether there exists
significant modification of the $\bar u -\bar d$ distribution in nuclei in a
parton recombination model. It should be noted that a finite $\bar u-\bar d$
distribution is theoretically possible in nuclei even if the sea is $SU(2)_f$
symmetric in the nucleon. In neutron-excess nuclei such as the tungsten, there
exist more $d$-valence quarks than $u$-valence quarks, so that more $\bar
d$-quarks are lost than $\bar u$-quarks are due to parton recombinations in the
small $x$ region. Our results suggest that the nuclear modification in the
tungsten is a 2--10 % effect on the $\bar u-\bar d$ distribution suggested by
the NMC data. Nuclear effects on the flavor asymmetric distribution could be an
interesting topic for future theoretical and experimental investigations.
