Polyaniline/Na+-montmorillonite (Na+-MMT) nanocomposites synthesized by in-situ intercalative polymerization of aniline into Na+-MMT are reported. The expansion distribution of basal spacing of the silicate layers upon the increase of the amount of aniline relative to Na+-MMT is, for the first time, estimated from the square of the full-width at half-maximum (FWHM2) of XRD patterns. According to the FT-IR frequency shift of the C-N stretching vibration, the change in the basal spacing of the silicate layers is closely related to the degree of hydrogen bonding between polyaniline and the silicate basal surface in a confined geometry.