An experimental study on metastable equilibria at T = 288 K in the quinary system Li2CO3 + Na2CO3 + K2CO3 + Li2B4O7 + Na2B4O7 + K2B4O7 + H2O was done by isothermal evaporation method. Metastable equilibrium solubilities and densities of the solution were determined experimentally. According to the experimental data, the metastable equilibrium phase diagram under the condition saturated with Li2CO3 was plotted, in which there are four invariant points; nine univariant curves; six fields of crystallization: K2CO3 . 3/2H(2)O, K2B4O7 . 5H(2)O, Li2B2O4 .16H(2)O, Na2B2O4 . 8H(2)O, Na2CO3 . 10H(2)O, NaKCO3 . 6H(2)O. Some differences were found between the stable phase diagram at T = 298 K and the metastable one at T = 288 K. (C) 2003 Elsevier Ltd. All rights reserved.