During the crystallization of gibbsite Al(OH)(3), which leads to the synthesis of alumina in the Bayer process, crystals go through a step of agglomeration. In this work, we present a study concerning the influence of different organic compounds, polycarboxylic acids and polyalcohols on the crystallization and agglomeration of gibbsite crystals. It has been determined that they act as crystal habit modifiers and inhibitors of the agglomeration occurring during the formation of alumina crystallites. Simply by following the kinetics of the reaction, it has been observed that polyalcohols are stronger inhibitors than polycarboxylic acids, which can be linked to the structure of gibbsite crystals. The influence of the characteristics of the additive, such as the number of carboxylic groups and the distance between them for polyacids, the stereochemistry and the length of the carbon chain in the case of polyalcohols, is demonstrated to have a significant effect.