Abstract The results of conventional powder X-ray diffraction and 29Si solid-state MAS NMR spectroscopy were used to investigate the distribution of Si atom defects in a silicalite optimized for the vapor-phase Beckmann rearrangement process. Powder diffraction data of the dehydrated sample were collected for carrying out accurate Rietveld analysis at room temperature, indicating orthorhombic symmetry of space group Pnma. The result of the 29Si MAS NMR spectrum analysis indicated that the number of Si atom defects in silicalite was 1.6 per unit cell. In addition, the result of Rietveld refinement suggested that the defects preferentially appeared at the T2, T3, and T6 sites, which were located along the wall of the straight channels of the MFI structure. The number of lattice defects estimated from the refined structural parameters was 1.5 per unit cell, which was consistent with that estimated from the 29Si MAS NMR analysis.