A phase equilibrium apparatus was designed to determine the solubilities of stearic acid and palmitic acid in subcritical water at different temperatures and pressures. The dissolution equilibrium time was measured. The effect of an ultrasonic field on dissolution equilibrium was also studied. The results showed that the maximum solubilities of stearic acid and palmitic acid were 0.136 g/100 g and 0.178 g/100 g in subcritical water at temperatures of 180 degrees C and 160 degrees C, respectively, and a pressure of 15 MPa for 30 mm. An ultrasonic field also clearly promoted the dissolution of fatty acids in subcritical water. The dissolution equilibrium time was shortened to 20 min using ultrasonic oscillation (250 W, 20 kHz). (C) 2013 Elsevier B.V. All rights reserved.