Alumina, which is a catalyst support, is obtained by boehmite calcination. This work aims to study boehmite precipitation and the impact of this step on alumina quality. Precipitation of boehmite is studied in a double-jet stirred tank and with a micro-mixer. These devices induce different mixing of the reagents and different evolution of the supersaturation. Precipitation is followed on-line with an optical apparatus based on multiple light scattering. Alumina obtained with micro-mixer presents significantly lower specific surface area, pore volume and mean pore diameter than the one obtained with the double jet reactor, showing a totally different crystallite aggregation. Using different types of micromixers at isosupersaturation, the results show that Reynolds number in the micro-mixer, stirring power in the receiving vessel and micro-mixer type have no effect on porosity and thus on aggregation, which could be explained by a supersaturation that is sufficiently high to prevent other parameters from having effects. Using double jet reactor, feeding time directly affects initial supersaturation, which level is lower than the one created in micro-mixer. For double jet precipitation, the textural properties are directly correlated to the initial supersaturation. Alumina obtained with the highest value of supersaturation with double-jet stirred tank has similar porosity value than the one obtained in micro-mixer. This supersaturation level would thus be a threshold beyond which other operating parameters have no effect. Aggregation would be directly controlled by initial supersaturation. Furthermore, it was shown that differences of alumina textures are correlated with different behaviors of backscattering levels. This technique allows the in situ characterization of aggregation differences, during precipitation, before the impact of filtration-washing-drying steps on aggregation. (C) 2015 Elsevier B.V. All rights reserved.