The secondary nucleation during gibbsite precipitation with seeds from sodium aluminate solution processed by ultrasound was examined by particle size distribution(PSD) analyses. Experiments indicate that at low temperature(＜65 ℃ ) and with low frequency ultrasound, the precipitation efficiency and also the secondary nucleation can be improved. Solution processed by low frequency ultrasound has more nuclei than common liquor does at low temperature. At 55 ℃, precipitation efficiency can he improved by 5.31 %, and the effect promoted by low frequency ultrasound decreases with the increase of temperature.