Raman spectroscopy was used to study the crystalline states of poly(trimethylene terephthalate) (PTT). There were significant spectral differences between the PTT melt and the crystallized PTT. The 909 cm(-1) band, associated with the C-C stretching of the trimethylene glycol residue, was found to be a suitable band for quantitative measurements of PTT crystallinity. Both the 847 and 1176 cm(-1) benzene ring breathing modes could be used as the internal reference bands, however, the use of the 1176 cm(-1) band was more sensitive to crystallinity changes. Two other C-C glycol residue stretching bands, 1116 and 1103 cm(-1), were found to relate to the crystalline and amorphous phases, respectively, from annealing experiment.