Nanosize molybdenum trisulfide, MoS3, was synthesized in a polyoxyethylene(2) nonylphenyl ether/cyclohexane/water microemulsion by acidifying ammonium tetrathiomolybdate solubilized in the water cores of inverse micelles. MoS3 was also prepared by thermal decomposition for comparison. X-ray diffraction, TEM, and electrochemical testing characterized the molybdenum trisulfide. By comparing the cyclic voltammetry results on MoS3 and S electrodes in lithium cells, the conclusions about the structure of MoS3 from previous research work have been confirmed. That is, the molybdenum trisulfide molecules were not a mixture of MoS2 and elemental S. Molybdenum trisulfide exists as Mo3S9 clusters, which are, in turn, linked by bridging SS bonds.