Relativistic two-component ab initio calculations through second-order Douglas-Kroll-Hess (DKH2) transformation are performed on Th+ and Th2+ ions. Spin-orbit-free calculations are done at SA-CASSCF and MS-CASPT2 levels. Spin-orbit coupled states are studied using effective mean-field operator. Spinorbit states of Th+, below 23000 cm(-1) are compared with experimental values. Relative separations between various energy levels depend on the amount of electron correlation included in the calculation. For Th2+, spin-orbit energy levels below 20000 cm(-1) agree well with the experimental levels. Transition properties of several spin-orbit states in case of Th2+ ion are predicted. (c) 2012 Elsevier B.V. All rights reserved.