Sodium ammonium tartrate (NAT) is an organic compound with the formula Na(NH4)[O2CCH(OH)CH(OH)CO2].

The salt is derived from tartaric acid by neutralizing with ammonia and with sodium hydroxide.

Louis Pasteur obtained enantiopure crystals of the tetrahydrate of NAT, via the process of spontaneous resolution.

[1] His discovery led to increased study of optical activity, which eventually was shown to have broad implications.

[2] Many modifications of this salt have been investigated by X-ray crystallography, including the racemate, which crystallizes as the monohydrate.