Orbital degrees of freedom have attracted much attention in the physics of 3d transition metal oxides. In particular a quantum effect is one of the recent important topics in orbital physics. Electron systems with t_2g degenerate orbitals are expected to have strong quantum effect, because the Jahn-Tellar coupling for t_2g orbitals is weaker than for the e_g orbitals. One of the most investigated t_2g systems is RTiO₃ (R= Y and La). YTiO₃ is a ferromagnet with T_c~30 K, whereas LaTiO₃ is an antiferromagnet with T_N~150 K. In this study we have studied orbital states in YTiO₃ and LaTiO₃ by means of NMR. We found that the NMR spectra in a single crystal of YTiO₃ can be explained if the 3d electron quadrupole moment is reduced from the expected value of the orbital ordering model based on the Hartree-Fock and GGA band calculations. This reduction is considered to come from the quantum fluctuation in the t_2g orbitals. We have also in LaTiO₃ examined the Ti NMR spectra based on the orbital liquid and ordering models. We showed that there is the large 3d electron quadrupole moment, indicating that the orbital liquid model is inappropriate. The NMR spectra are explained by the orbital ordering model as (d_xy+d_yz+d_zx)/√3 due to a crystal field effect.