Gallium(III) chloride is an inorganic chemical compound with the formula GaCl₃ which forms a monohydrate, GaCl₃·H₂O. Solid gallium(III) chloride is a deliquescent colorless crystals and exists as a dimer with the formula Ga₂Cl₆. It is colourless and soluble in virtually all solvents, even alkanes, which is unusual for a metal halide. It is the main precursor to most derivatives of gallium and a reagent in organic synthesis.

As a Lewis acid, GaCl₃ is milder than aluminium chloride. It is also easier to reduce than aluminium chloride. The coordination chemistry of Ga(III) and Fe(III) are similar, so gallium(III) chloride has been used as a diamagnetic analogue of ferric chloride.

Gallium(III) chloride can be prepared from the elements by heating gallium metal in a stream of chlorine at 200 °C and purifying the product by sublimation under vacuum.

It can also be prepared from by heating gallium oxide with thionyl chloride:

Gallium metal reacts slowly with hydrochloric acid, producing hydrogen gas. Evaporation of this solution produces the monohydrate.

As a solid, it adopts a bitetrahedral structure with two bridging chlorides. Its structure resembles that of aluminium tribromide. In contrast AlCl₃ and InCl₃ feature contain 6 coordinate metal centers. As a consequence of its molecular nature and associated low lattice energy, gallium(III) chloride has a lower melting point vs the aluminium and indium(III) halides. The formula of Ga₂Cl₆ is often written as Ga₂(μ-Cl)₂Cl₄.

In the gas-phase, the dimeric (Ga₂Cl₆) and trigonal planar monomeric (GaCl₃) are in a temperature-dependent equilibrium, with higher temperatures favoring the monomeric form. At 870 K, all gas-phase molecules are effectively in the monomeric form.

In the monohydrate, the gallium is tetrahedrally coordinated with three chlorine molecules and one water molecule.