Some uranium (U(VI) and U(V)) triatomic molecules and cations with the general formula XUY (X,Y = C,N,O) and a charge varying from O to +2 have been studied using multiconfigurational second-order perturbation theory (CASSCF/CASPT2) and Density Functional Theory (DFT). Geometry optimizations and infrared harmonic frequency calculations have been carried out and a comparison with available experimental data has been performed. This study shows that CASSCF/CASPT2 is capable of handling actinide systems, where multiconfiguratioanl and relativistic effects are essential.