  The sensitivity of the ATLAS experiment to the top-quark rare decay via
flavor-changing neutral currents $t \rightarrow Zq$ ($q$ represents $c$ and $u$
quarks) has been studied at $\sqrt{s}$=14 TeV in two decay modes:
  1.The pure leptonic decay of gauge bosons: $t\bar{t} \rightarrow ZqWb
\rightarrow l^{+} l^{-} j l^{\pm} \nu b$ , (l=e, $\mu$).
  2.The leptonic decay of Z bosons and hadronic decay of W bosons: $t\bar{t}
\rightarrow ZqWb \rightarrow l^{+} l^{-} jjjb$ , (l=e, $\mu$).
  The dominant backgrounds $Z+jets$, $WZ$ and $t\bar{t}$ have been analysed.
The signal and backgrounds were generated via PYTHIA 5.7, and simulated and
analysed using ATLFAST 2.14. A branching ratio for $t \rightarrow Zq$ as low as
2.0x10$^{-4}$ for the leptonic mode and 5.9x10$^{-4}$ for hadronic mode could
be discovered at the 5$\sigma$ level with an integrated luminosity of 100
fb$^{-1}$.
