  We present a simple extension of MSSM which provides a unified picture of
cosmological baryon asymmetry and dark matter. Our model introduces a gauge
singlet field $N$ and a color triplet field $X$ which couple to the
right--handed quark fields. The out--of equilibrium decay of the Majorana
fermion $N$ mediated by the exchange of the scalar field $X$ generates adequate
baryon asymmetry for $M_N \sim 100$ GeV and $M_X \sim$ TeV. The scalar partner
of $N$ (denoted $\tilde{N}_1$) is naturally the lightest SUSY particle as it
has no gauge interactions and plays the role of dark matter. $\tilde{N}_1$
annihilates into quarks efficiently in the early universe via the exchange of
the fermionic $\tilde{X}$ field. The model is experimentally testable in (i)
neutron--antineutron oscillations with a transition time estimated to be around
$10^{10}$ sec, (ii) discovery of colored particles $X$ at LHC with mass of
order TeV, and (iii) direct dark matter detection with a predicted cross
section in the observable range.
