Abstract: The phase equilibrium of aldol condensation reaction between citral and acetone catalyzed by aqueous sodium hydroxide solution was studied. Some phase diagrams of acetone-citral-water system snd acetone-pseudoinone-water system were presented, while the solubility curves of acetone-citral-water containing a few percent of sodiun hydroxide were measured by an improved gradual titration method. According to the results obtained, the mechanism of this aldol condensation reaction was analysed.