Shock compression measurements of lithium niobate single crystals are carried out up to 121 GPa using the gun method. Hugoniot elastic limits are found to be 2.4 and 6.6 GPa with the shock propagation direction along [0001] and [112¯0], respectively, reflecting a remarkable elastic anisotropy. A phase transition accompanied by a discontinuous volume decrease is induced at the shock pressure of 32.6±0.6 GPa. The zero‐pressure volume of the high‐pressure phase is estimated to be smaller by 20.5% than that of the low‐pressure‐phase lithium niobate. The observed large volume decrease strongly suggests considerable change in the bond character with the phase tranformation.