A series of new layered gallium(III) and indium(III) phosphonates, phenylarsonates and phenylphosphinates have been prepared and characterised. The methylphosphonate, phenylphosphonate and phenylarsonate derivatives of gallium(III) possess a metal to ligand ratio of 1 ∶ 1 and properties consistent with the formulation Ga(OH)(O3XR) (where X = P or As for R = C6H5, and where X = P for R = CH3), whereas the benzylphosphonate derivative forms the monohydrate Ga(OH)(O3XCH2C6H5)·H2O. The corresponding phosphinate derivative of gallium(III) has a metal to ligand ratio of 1 ∶ 2 with the formulation Ga(OH)(O2P(H)C6H5)2. The gallium compounds all contain a hydroxo group bonded to the metal, unlike the corresponding indium(III) compounds. The phenylphosphonate and phenylarsonate derivatives of indium(III) have a 1 ∶ 2 metal to ligand ratio and formula In(O3XR)(O2X(OH)R)·H2O (where R = C6H5 or CH2C6H5 when X = P and R = C6H5 when X = As), where the ligand is present as both a mono- and di-anion. The methylphosphonate of indium(III) has the unexpected formulation In2(O3PCH3)3·2H2O whereas the indium(III) phenylphosphinate compound is In(O2P(H)C6H5)3. These compounds were characterized by elemental analysis, thermal gravimetry, X-ray powder diffraction (XRD) and solid state 31P/13C MAS NMR spectroscopy. Powder XRD measurements indicate these compounds contain layered solid state structures.