The effect of an additive prepared from fatty acid surface active agent and heneicosane on two-stage seed precipitation process and Al2O3 production was studied.The results showed that the additive，with concentration of 60×10-6g·L-1，enhanced remarkably the precipitation process and improved the quality of Al（OH）3 and Al2O3.The precipitation rate of sodium aluminate solution increased by 2%，and the percentage of <45μm particles of Al（OH）3 and Al2O3 reduced by about 7% and 6.7%

respectively by adding the additive.The SEM photographs indicated that the additive could accelerate growth，agglomeration of Al（OH）3 particles and the Al（OH）3 particles were in the shape of globular crystals.The mechanism of additive effect was also studied.