The interaction of H2S gas with aqueous ammonium heptamolybdate solution in the presence of diethylenetriamine (dien) led to the formation of diethylenetriammonium tetrathiomolybdate crystals. The elemental analyses, UV-Visible, IR, and 1H NMR spectra suggested the presence of organic cation and (MoS4)2- moiety. The 1H NMR revealed the presence of two sets of symmetrical A2X2 multiple patterns. The compound crystallizes in the monoclinic system with space group Pn, a = 7.196(6), b = 7.532(3), c = 11.525(10) Å, α = 90°, β = 90.17(3)°, γ = 90°, V = 624.78(8) Å3, and Z = 2, wR1 = 0.0261 and wR2 = 0.0698. The structure consists of tetrahedral tetrathiomolybdate anions, which form an extended three-dimensional network in the solid state with Mo-S⋯H-N hydrogen bonding with the organic cation.