Abstract: The crystal structure of synthetic deuterated kaolinite was refined by Rietveld analysis using time-of-flight (TOF) neutron powder diffraction data. For non-hydrogen atoms, C1 symmetry was assumed. Starting models were tested in which only the direction of O-D vectors was varied. The constraints were introduced to all Al-O, Si-O and O-D bonds. The refinement adopting the former gives P1(C1), a = 5.169(1) Å, b = 8.960(2) Å, c = 7.410(2) Å, α = 91.26(2)°, β = 104.99(2)°, γ = 89.93(1)°, Rwp = 3.17%, RI = 5.78% and S = 1.34 with constraints of l(Al-O) = 1.93 ± 0.05 Å, l(Si-O) = 1.62 ± 0.03 Å and l(D-O) = 0.95 ± 0.15 Å. The inner O-D vector points toward the tetrahedral sheet. All inner-surface O-D groups form H bonding with basal O atoms in the next kaolinite layers. The results agreed with those obtained from natural kaolinite.