Abstract: During the seed precipitation process of sodium aluminate solution, adding an anionic surfactant derived from unsaturated fatty acid in the solution can intensify the decomposition process so as to improve the quality of final products. Experimental results indicated that the decomposed portion of sodium aluminate can increase by about 5%, with the average grain size and strength of aluminum hydroxide as final product increase by 2% and about 5%, respectively, if adding in 280 mg/l of the surfactant. The fact implies that there is an obvious physico-chemical change caused by the surfactant added in the solution. With the viscosity, surface tension and conductivity of the solution tested, the functional mechanism of the surfactant is discussed and elucidated.