Raman spectroscopy has been applied for the rapid and nondestructive monitoring of the interlayer structure of sodium montmorillonite (MMT) clay modified by ditetradecyl dimethyl ammonium (DDA(+)) bromide. This work demonstrates that a detailed analysis of Raman spectra in the fingerprint region (600-1600 cm(-1)), in combination with model simulation, allows one to distinguish different conformational states of DDA(+) in the interlayer space of the modified clay, namely, a liquidlike state but rich in trans conformers, disordered conformational states, and a crystallike conformation appearing at increasing modifier content. These conformations differ in the angle between their alkyl chains, the relative content of trans and gauche conformers and the relative length of trans segments. The shape and width of the Raman band at 1300 cm(-1) and the peak intensity ratio I-1088/I-1064 can be used for a qualitative analysis of the ratio of gauche/trans conformers. The integral intensity ratios I*(1064)/I*(1300) and I*(1300)/I*(705) help to determine the proportion of trans conformers and the content of the modifier in the clay, respectively, thereof providing quantitative characterization of the modified clay (conformational reorganization and modifier content). Noteworthy, the transition from a liquidlike to crystal-like conformation is further supported by the splitting of the symmetric C-C stretching Raman band of the trans segments within the alkyl chains at 1133 cm(-1) (liquidlike conformation) into two modes at 1124 and 1135 cm(-1) corresponding to two parallel trans chains of nonequivalent lengths (crystal-like conformation).