A new polymorph of Mo3S4 was synthesized at 13 GPa and 1450 degrees C from a stoichiometric mixture of elements. It crystallizes in a triclinic unit cell (space group P (1) over bar (No. 2)) with cell constants of a = 6.364(2) angstrom, b = 6.608(2) angstrom, c = 6.809(2) angstrom, alpha = 103.899(3)degrees, beta = 117.753(3) degrees, gamma = 103.958(3) degrees, and V= 224.25(13) angstrom(3). The structure of Mo3S4 is composed of edge- and face-sharing MoS6 octahedra. It was closely related to the structure of MMo2S4 type compounds (M = V, Cr, Fe, and Co). Mo3S4 can be regarded as a derivative with M = Mo. The calculated density of 6.160 g/cm(3) was much larger than 5.191 g/cm(3) of famous polymorphic Mo6S8 (Chevrel phase). Mo3S4 was metallic and did not show any superconducting transition down to 2 K. The bond-valence sums suggested that Mo3S4 can be classified in the class HI B of mixed-valence compounds; all Mo ions have a similar nonintegral valence. Electronic structure calculations revealed that the conduction band of Mo3S4 contains much contribution of the relatively narrow Mo 4d bands as well as the bands composed of hybridized Mo4d-S3d orbitals.