  We calculate QCD correction to the neutralino annihilation cross section into
quark anti-quark final state and discuss its implications to the calculation of
neutralino relic density. We see that the QCD correction enhances the
pair-annihilation cross section by O(10 %) when final-state quarks are
non-relativistic. Consequently, when the lightest neutralinos dominantly
annihilate into a t\bar{t} pair, the relic density of the lightest neutralino
is significantly affected by the QCD correction, in particular when the
lightest-neutralino mass is close to the top-quark mass.
