The complexes of 2,3,4-trimethoxybenzoic acid with Tb(III), Dy(III), Ho(III), Er(III), Tm(III), Yb(III), Lu(III) and Y(III) are crystalline, anhydrous salts with colours typical of the M(III) ions. The carboxylate group is probably a bidenate, chelating ligand. The thermal stabilities of the complexes were examined under an air atmosphere in the temperature range 293–1273 K. The solubility in water at 293 K for all the heavy lanthanide(III) and yttrium(III) complexes are in the order of 10-3 mol dm-3. The magnetic moments of the complexes were determined in the temperature range 77–300 K.