From pH and conductance measurements it is concluded that mandelic acid is a good chelating agent for aluminium. Three chelates corresponding to 1:1, 1:2 and 1:3 Formulae are formed. The chelate of composition 1:1 is formed at a lower pH value, while 1:2 and 1:3 chelates, which occur at pH 6.5 and 7.8 respectively, are more stable than 1:1 chelate. The chelation takes place easily on account of the close proximity of the acidic and electron--donating groups, a fact which is essential for formation of the ring containing the metal atom.