  We compute the thermal axino production rate in supersymmetric QCD to leading
order in the gauge coupling. Using hard thermal loop resummation and the
Braaten-Yuan prescription, we obtain a finite result in a gauge-invariant way,
which takes into account Debye screening in the hot quark-gluon-squark-gluino
plasma. The relic axino density from thermal reactions in the early Universe is
evaluated assuming the axino is the lightest supersymmetric particle and stable
due to R-parity conservation. From the comparison with the WMAP results, we
find that axinos could provide the dominant part of cold dark matter, for
example, for an axino mass of 100 keV and a reheating temperature of 10^6 GeV.
