The nucleation in the supersaturated solutions of ammonium tetramolybdate prepared from acidified ammonium heptamolybdate solutions is studied in this paper. The nucleation rates as indicated by the induction period were measured. Effects of temperature and supersaturation on the nucleation rate were discussed. The results in good accordance with the classical nucleation theory show that the nucleation rate of ammonium tetramolybdate increases with increases of temperature and supersaturation. The interfacial tensions of homogeneous nucleation and heterogeneous nucleation decrease with increase of temperature in the range of 295.15K to 311.15K.