Diphosphorus trisulfide (sometimes called phosphorus trisulfide) is a hypothetical phosphorus sulfide with the formula of . In contrast, the formal dimer P<sub>4</sub>S<sub>6</sub> is well-known.
Early reports that diphosphorous trisulfide could be formed by heating red phosphorus and sulfur were shown to be incorrect by Helff in 1893. Its existence was again reported by Ralston and Wilkinson in 1928. In 1959, Pitochelli and Audrieth attempted to prepare via the reaction , instead obtaining an equimolar mixture of and following recrystallization in carbon disulfide. In 1997, Lohr and Sundholm published a theoretical analysis of the potential structures of this molecular substance.
In 2017, Xiao proposed that a 2D crystallisation of was possible based on computer simulations. Xiao suggested that nanoribbons and nanotubes of the material may have applications in semiconductor electronics.