Diffusion coefficient of lithium ions in Li6.5La3Zr1.5Ta0.5O12 (LLZTO) single crystal is measured using 'Li pulse( field gradient nuclear magnetic resonance (PFG-NMR) spectroscopy in the temperature range from 298 K tc 353 K. The Li diffusion coefficient in LLZTO is evaluated to be 1.9 x 10(-13) m(2) s(-1) at 298 K with the activation energy of 0.43 eV. The ionic conductivity of LLZTO single crystal is measured by impedance spectroscopy, whicl gives 7 x 10(-4) S cm(-1) at 298 K with the activation energy of 0.43 eV. The diffusion coefficient obtained by PFG NMR is lesser than the diffusion coefficient calculated from ionic conductivity using Nernst-Einstein relation The small discrepancy gives the Haven ratio of 0.4, which suggests a correlated migration of the lithium ions it the tetrahedral and octahedral sites in LLZTO. To compare the present result with previous reports, the diffusior time (d) dependence is carefully checked in PFG-NMR not only for the single crystal but also the crushes powdered samples, which revealed no significant dependence in the single crystal but small dependence in tht crushed samples which may be due to the restricted diffusion in the powder grains.