In the system Bi2O3---MoO3 the following compounds were identified: 1. (1) Bi2O3 · 3MoO3 = Bi2(MoO4)3 m.p. 676 °C 2. (2) Bi2O3 · MoO3 = Bi2MoO6 = (BiO)2MoO4 m.p. 938 °C 3. (3) 3Bi2O3 · MoO3 = Bi6MoO12 m.p. 995 °C These compounds were found by investigation of the phase diagram of the Bi2O3---MoO3 binary system by means of thermal analysis. X-ray studies of sintered mixtures in this system confirmed the existence of the three compounds. A compound Bi2O3 · 2MoO3 could not be detected.