We have established highly anisotropic features of the piezooptical coefficient behavior in L-lysine monohydrochloride dihydrate (LLMHCl) single crystals (a semiorganic material with space group P21). These coefficients show substantial anisotropy for the diagonal and off-diagonal tensor coefficients. The XRD analysis, FTIR, optical and FT Raman spectra were performed. Following the obtained data, principal role of the phonon sub-system was established.