Raman spectroscopy and density functional theory calculations of beta-D-galactopyranose. Raman spectra of alpha- and beta-D-galactopyranose were measured in liquid n-C(5)H(12) at room temperature. The experimental spectral patterns, especially the relative intensities of the six fundamental bands, were analyzed and compared with the calculated ones obtained by the density functional theory method B3LYP/6-31G**. To simulate the influence of polarization on Raman scattering, the normal mode analysis was employed to calculate the intensity-weighted band positions. Besides the six fundamental bands at 1071, 1081, 1090, 1105, 1130 and 1157 cm(-1), it is found that the band at 960 cm(-1) is mostly derived from the C-C stretching vibration of C-O-C and that there exist many bands with their relative intensities differing considerably from those in liquid n-C(5)H(12). The higher energy bands are mainly from C-H deformation modes of C-H bond. The results demonstrate the Raman spectroscopy is a useful tool to study the structure of sugars and their hydrogen-bonded aggregates. The assignments of the observed spectral patterns were made, which are consistent with the previous literatures. Our results suggested that the beta-d-galactopyranose molecules should be in the anti-parallel dimer form rather than the (C4)-type parallel form as the alpha-form in liquid n-C(5)H(12). The anti-parallel dimer form of beta-d-galactopyranose might be a basic conformation for forming other biological aggregates such as beta-d-glucan and beta-d-fructan.