  The decay widths of top quark to S-wave $b\bar{c}$ and $b\bar{b}$ bound
states are evaluated at the next-to-leading(NLO) accuracy in strong
interaction. Numerical calculation shows that the NLO corrections to these
processes are remarkable. The quantum chromodynamics(QCD) renormalization scale
dependence of the results are obviously depressed, and hence the uncertainties
lying in the leading order calculation are reduced.
