Abstract Potentiometric, conductometric and preparative studies of beryllium 2-hydroxy-3-naphthoate systems indicate the formation of two complexes; the 1:1 complex predominates at a pH of about 5.5 and the 1:2 complex in the ionic form at pH 8–9. In aqueous medium the 1:2 complex is precipitated first by the addition of the potassium salt of the acid to a beryllium sulphate solution, which then changes into the 1:1 complex by the addition of one mole of alkali. In 50% alcoholic medium in which complexes are soluble the formation of 1:1 complex is only indicated in acidic solutions. The stability constants in 50% alcohol of the complexes have been calculated by Bjerrum's method. For comparison, stability constants for salicylate and sulpho-salicylate complexes were also determined under identical conditions. Stability constants k were found to be: log k 1 = 11.98, log k 2 = 7.92; log k 1 = 12.45, log k 2 = 8.50; log k 1 = 11.52, log k 2 = 8.90, respectively for 2-hydroxy-3-naphthoate, salicylate and sulpho-salicylate complexes. Dissociation constants of the acids were determined in 50% alcohol using a hydrogen electrode. New compounds: BeC 11H 6O 3·2 H 2O, H 2Be(C 11H 6O 3) 2 and K 2Be(C 11H 6O 3) 2 were isolated.