Crystals of bis-chloromethyl-phosphinic acid ((CH ₂ Cl) ₂ POOH) are studied by attenuated total reflection (ATR) and Raman spectroscopy supported by X-Ray diffraction. The bands recorded in the ATR and in Raman spectra have the same wavenumbers within experimental uncertainty. It is in agreement with the X-Ray diffraction results which show that the molecules in crystals form infinite chains through hydrogen bonds and there is no center of inversion. The parameters of the unit cell, the bond lengths and angles, and the distance between two oxygen atoms in hydrogen bond bridges are determined. The spectral features and the intermolecular distance between oxygen atoms are characteristic for a strong hydrogen bonded system.