  The renormalization of the scalar diquark operator and its anomalous
dimension is calculated at two-loop order in QCD, enabling higher-order QCD
studies of diquarks. As an application of our result, the two-loop diquark
anomalous dimension in the $\bar{{\rm MS}}$ scheme is used to study the QCD
renormalization scale dependence of diquark matrix elements of the $\Delta S=1$
effective weak Hamiltonian.
