The FTIR spectra of aragonites in outer and inner layers of thirteen species of mollusk shells were systematically measured, and the frequency variations of frequency 1, frequency 2 and frequency 4 bands of the aragonites with the positions of shell layers were analyzed. The results showed that the frequency of v2 band differed in different species of shells and the positions of shell layers, but the frequencies of the other two bands were not altered, and had the same values with synthetic aragonites. In the same species of shells, the frequency of frequency 2 band in inner layers was greater than that in outer layers, and the frequency shift of frequency 2 band between inner and outer layers was in the range of 0.5 x 4.5 cm(-1) in all studied samples. The detection of frequency shift of frequency 2 band in different layers of aragonitic mollusk shell was first reported in this paper.