Abstract The polarized Raman spectrum of a single crystal of SnHPO 4 has been obtained in order to ascertain the vibrational characteristics of HPO 2− 4 dimers in a known configuration. Bands due to hydroxyl, OH, stretching, POH bending and the hydrogen bond were observed in addition to most of the predicted lattice modes. The OH stretching mode was observed at 2730 cm −1, the in-plane POH bend at 1275 cm −1 and the out-of-plane POH bend at 818 cm −1. A band of 55 cm −1 is assigned, on the basis of its deuterium shift, to a deformation of the hydrogen bond. Very low frequency bands at 18 and 30 cm −1 reflect the layer structure of SnHPO 4 in which intra-layer forces are strong and inter-layer (hydrogen bonds) forces are weak.