Physical properties derived from proton-dynamics in hydrogenbonded molecular crystals are discussed from two aspects. First, the effect of a static or dynamic modulation is discussed on conduction property of Ni(dmit)2caused by a hydrogen-bonded counter cation system. An anomaly was observed in conduction property of Ni(dmit)2· Lin(H2O)msalt which is presumably due to a change in the hydration scheme. Second, physical properties of hydrogen-bonded tautomeric molecules are examined in the case of 3-hydroxy-phenalenone (1) and its derivative (2). No dynamic processes were detected in the crystals of1, although the crystal is polar and exhibits second harmonic generation. On the other hand the crystal of 2carboxy derivative 2 behaves as paraelectrics at room temperature at ambient pressure with a phase transition to an antiferroelectric phase at 40 K. This remarkable property is ascribed to the rapid tautomerization mediated by 2-carboxyl substituent coupling with proton-transfer in intermolecular bifurcated hydrogen bonds.