Single crystals of L-histidine phosphite (L-Hist center dot H3D D-3) have been grown from aqueous solution by slow cooling method. The results of elemental analysis, of X-ray-diffraction studies of the crystal structure, and the habitus of the obtained crystals are given. The elastic and piezoelectric coefficients have been measured on the plates with the (010) natural faces by the method of electromechanical resonance for stretching vibrations in the temperature range 295-340 K. Elastic compliance values s (33) and s (22) and the corresponding elastic-moduli values, piezoelectric coefficients d (23) and d (22), coefficients of electromechanical coupling, and temperature coefficient of the resonance frequency are obtained. A comparison is given with other crystals, which are compounds of amino acids with phosphorous or phosphoric acid.