The equilibrium structures and anharmonic force fields of the SiOH and HSiO radicals in their (2)A' ground electronic state have been determined from large-scale ab initio calculations using the coupled-cluster method, RCCSD(T), with basis sets of double- through quintuple-zeta quality. The vibrational-rotational energy levels of both species were calculated by the perturbational and variational approach, and the spectroscopic constants were then determined. The rotational and centrifugal distortion constants of the HSiO radical are in good agreement with the experimental data. The predicted spectroscopic constants of the SiOH radical can be useful in the future detection of this species by vibrational-rotational spectroscopy.