  The sensitivity of ATLAS experiment to the top-quark rare decay via flavor-
changing neutral currents t \to Zq (q represents c and u quarks) have been
studied at \sqrt{s}= 14 TeV in two decay modes:
  1. The pure leptonic decay of gauge bosons: t\bar{t} \to ZqWb \to l^{+} l^{-}
j l^{+-} nu j_{b} (l=e, mu)
  2. The leptonic decay of Z bosons and hadronic decay of W bosons t\bar{t} \to
ZqWb \to l^{+} l^{-} jjjj_{b} (l=e, mu)
  The dominant backgrounds Z-jets, Zw and t\bar{t} has been analysed. The
signal and backgrounds were generated via PYTHIA 5.7, simulated and analysed
using ATLFAST 2.14. A branching ratio for t \to Zq as low as 1.1x1-^{4} for the
leptonic mode and 2.3x10^{4} for hadronic mode could be discovered at the
5\sigma level with an integrated luminosity of 10^{5} pb^{-1}.
